Jeffrey added Multi-MSI support to the pci-hyperv driver by the 4 patches:
08e61e861a0e ("PCI: hv: Fix multi-MSI to allow more than one MSI vector")
455880dfe292 ("PCI: hv: Fix hv_arch_irq_unmask() for multi-MSI")
b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
a2bad844a67b ("PCI: hv: Fix interrupt mapping for multi-MSI")
It turns out that the third patch (b4b77778ecc5) causes a performance
regression because all the interrupts now happen on 1 physical CPU (or two
pCPUs, if one pCPU doesn't have enough vectors). When a guest has many PCI
devices, it may suffer from soft lockups if the workload is heavy, e.g.,
see https://lwn.net/ml/linux-kernel/[email protected]/
Commit b4b77778ecc5 itself is good. The real issue is that the hypercall in
hv_irq_unmask() -> hv_arch_irq_unmask() ->
hv_do_hypercall(HVCALL_RETARGET_INTERRUPT...) only changes the target
virtual CPU rather than physical CPU; with b4b77778ecc5, the pCPU is
determined only once in hv_compose_msi_msg() where only vCPU0 is specified;
consequently the hypervisor only uses 1 target pCPU for all the interrupts.
Note: before b4b77778ecc5, the pCPU is determined twice, and when the pCPU
is determinted the second time, the vCPU in the effective affinity mask is
used (i.e., it isn't always vCPU0), so the hypervisor chooses different
pCPU for each interrupt.
The hypercall will be fixed in future to update the pCPU as well, but
that will take quite a while, so let's restore the old behavior in
hv_compose_msi_msg(), i.e., don't reuse the existing IRTE allocation for
single-MSI and MSI-X; for multi-MSI, we choose the vCPU in a round-robin
manner for each PCI device, so the interrupts of different devices can
happen on different pCPUs, though the interrupts of each device happen on
some single pCPU.
The hypercall fix may not be backported to all old versions of Hyper-V, so
we want to have this guest side change for ever (or at least till we're sure
the old affected versions of Hyper-V are no longer supported).
Fixes: b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
Co-developed-by: Jeffrey Hugo <[email protected]>
Signed-off-by: Jeffrey Hugo <[email protected]>
Co-developed-by: Carl Vanderlip <[email protected]>
Signed-off-by: Carl Vanderlip <[email protected]>
Signed-off-by: Dexuan Cui <[email protected]>
---
v1 is here:
https://lwn.net/ml/linux-kernel/[email protected]/
Changes in v2:
round-robin the vCPU for multi-MSI.
The commit message is re-worked.
Added Jeff and Carl's Co-developed-by and Signed-off-by.
Changes in v3:
Michael Kelley kindly helped to make a great comment, and I added the
comment before hv_compose_msi_req_get_cpu(). Thank you, Michael!
Rebased to Hyper-V tree's "hyperv-fixes" branch:
https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-fixes
Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
through the Hyper-V tree because it's rebased to another hv_pci patch (which
only exists in the Hyper-V tree for now):
e70af8d040d2 ("PCI: hv: Fix the definition of vector in hv_compose_msi_msg()")
BTW, Michael has some other hv_pci patches, which would also need go through
the Hyper-V tree:
https://lwn.net/ml/linux-kernel/1666288635-72591-1-git-send-email-mikelley%40microsoft.com/
drivers/pci/controller/pci-hyperv.c | 90 ++++++++++++++++++++++++-----
1 file changed, 75 insertions(+), 15 deletions(-)
diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index ba64284eaf9f..fa5a1ba35a82 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -1613,7 +1613,7 @@ static void hv_pci_compose_compl(void *context, struct pci_response *resp,
}
static u32 hv_compose_msi_req_v1(
- struct pci_create_interrupt *int_pkt, const struct cpumask *affinity,
+ struct pci_create_interrupt *int_pkt,
u32 slot, u8 vector, u16 vector_count)
{
int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE;
@@ -1631,6 +1631,35 @@ static u32 hv_compose_msi_req_v1(
return sizeof(*int_pkt);
}
+/*
+ * The vCPU selected by hv_compose_multi_msi_req_get_cpu() and
+ * hv_compose_msi_req_get_cpu() is a "dummy" vCPU because the final vCPU to be
+ * interrupted is specified later in hv_irq_unmask() and communicated to Hyper-V
+ * via the HVCALL_RETARGET_INTERRUPT hypercall. But the choice of dummy vCPU is
+ * not irrelevant because Hyper-V chooses the physical CPU to handle the
+ * interrupts based on the vCPU specified in message sent to the vPCI VSP in
+ * hv_compose_msi_msg(). Hyper-V's choice of pCPU is not visible to the guest,
+ * but assigning too many vPCI device interrupts to the same pCPU can cause a
+ * performance bottleneck. So we spread out the dummy vCPUs to influence Hyper-V
+ * to spread out the pCPUs that it selects.
+ *
+ * For the single-MSI and MSI-X cases, it's OK for hv_compose_msi_req_get_cpu()
+ * to always return the same dummy vCPU, because a second call to
+ * hv_compose_msi_msg() contains the "real" vCPU, causing Hyper-V to choose a
+ * new pCPU for the interrupt. But for the multi-MSI case, the second call to
+ * hv_compose_msi_msg() exits without sending a message to the vPCI VSP, so the
+ * original dummy vCPU is used. This dummy vCPU must be round-robin'ed so that
+ * the pCPUs are spread out. All interrupts for a multi-MSI device end up using
+ * the same pCPU, even though the vCPUs will be spread out by later calls
+ * to hv_irq_unmask(), but that is the best we can do now.
+ *
+ * With current Hyper-V, the HVCALL_RETARGET_INTERRUPT hypercall does *not*
+ * cause Hyper-V to reselect the pCPU based on the specified vCPU. Such an
+ * enhancement is planned for a future version. With that enhancement, the
+ * dummy vCPU selection won't matter, and interrupts for the same multi-MSI
+ * device will be spread across multiple pCPUs.
+ */
+
/*
* Create MSI w/ dummy vCPU set targeting just one vCPU, overwritten
* by subsequent retarget in hv_irq_unmask().
@@ -1640,18 +1669,39 @@ static int hv_compose_msi_req_get_cpu(const struct cpumask *affinity)
return cpumask_first_and(affinity, cpu_online_mask);
}
-static u32 hv_compose_msi_req_v2(
- struct pci_create_interrupt2 *int_pkt, const struct cpumask *affinity,
- u32 slot, u8 vector, u16 vector_count)
+/*
+ * Make sure the dummy vCPU values for multi-MSI don't all point to vCPU0.
+ */
+static int hv_compose_multi_msi_req_get_cpu(void)
{
+ static DEFINE_SPINLOCK(multi_msi_cpu_lock);
+
+ /* -1 means starting with CPU 0 */
+ static int cpu_next = -1;
+
+ unsigned long flags;
int cpu;
+ spin_lock_irqsave(&multi_msi_cpu_lock, flags);
+
+ cpu_next = cpumask_next_wrap(cpu_next, cpu_online_mask, nr_cpu_ids,
+ false);
+ cpu = cpu_next;
+
+ spin_unlock_irqrestore(&multi_msi_cpu_lock, flags);
+
+ return cpu;
+}
+
+static u32 hv_compose_msi_req_v2(
+ struct pci_create_interrupt2 *int_pkt, int cpu,
+ u32 slot, u8 vector, u16 vector_count)
+{
int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE2;
int_pkt->wslot.slot = slot;
int_pkt->int_desc.vector = vector;
int_pkt->int_desc.vector_count = vector_count;
int_pkt->int_desc.delivery_mode = DELIVERY_MODE;
- cpu = hv_compose_msi_req_get_cpu(affinity);
int_pkt->int_desc.processor_array[0] =
hv_cpu_number_to_vp_number(cpu);
int_pkt->int_desc.processor_count = 1;
@@ -1660,18 +1710,15 @@ static u32 hv_compose_msi_req_v2(
}
static u32 hv_compose_msi_req_v3(
- struct pci_create_interrupt3 *int_pkt, const struct cpumask *affinity,
+ struct pci_create_interrupt3 *int_pkt, int cpu,
u32 slot, u32 vector, u16 vector_count)
{
- int cpu;
-
int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE3;
int_pkt->wslot.slot = slot;
int_pkt->int_desc.vector = vector;
int_pkt->int_desc.reserved = 0;
int_pkt->int_desc.vector_count = vector_count;
int_pkt->int_desc.delivery_mode = DELIVERY_MODE;
- cpu = hv_compose_msi_req_get_cpu(affinity);
int_pkt->int_desc.processor_array[0] =
hv_cpu_number_to_vp_number(cpu);
int_pkt->int_desc.processor_count = 1;
@@ -1715,12 +1762,18 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
struct pci_create_interrupt3 v3;
} int_pkts;
} __packed ctxt;
+ bool multi_msi;
u64 trans_id;
u32 size;
int ret;
+ int cpu;
+
+ msi_desc = irq_data_get_msi_desc(data);
+ multi_msi = !msi_desc->pci.msi_attrib.is_msix &&
+ msi_desc->nvec_used > 1;
/* Reuse the previous allocation */
- if (data->chip_data) {
+ if (data->chip_data && multi_msi) {
int_desc = data->chip_data;
msg->address_hi = int_desc->address >> 32;
msg->address_lo = int_desc->address & 0xffffffff;
@@ -1728,7 +1781,6 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
return;
}
- msi_desc = irq_data_get_msi_desc(data);
pdev = msi_desc_to_pci_dev(msi_desc);
dest = irq_data_get_effective_affinity_mask(data);
pbus = pdev->bus;
@@ -1738,11 +1790,18 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
if (!hpdev)
goto return_null_message;
+ /* Free any previous message that might have already been composed. */
+ if (data->chip_data && !multi_msi) {
+ int_desc = data->chip_data;
+ data->chip_data = NULL;
+ hv_int_desc_free(hpdev, int_desc);
+ }
+
int_desc = kzalloc(sizeof(*int_desc), GFP_ATOMIC);
if (!int_desc)
goto drop_reference;
- if (!msi_desc->pci.msi_attrib.is_msix && msi_desc->nvec_used > 1) {
+ if (multi_msi) {
/*
* If this is not the first MSI of Multi MSI, we already have
* a mapping. Can exit early.
@@ -1767,9 +1826,11 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
*/
vector = 32;
vector_count = msi_desc->nvec_used;
+ cpu = hv_compose_multi_msi_req_get_cpu();
} else {
vector = hv_msi_get_int_vector(data);
vector_count = 1;
+ cpu = hv_compose_msi_req_get_cpu(dest);
}
/*
@@ -1785,7 +1846,6 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
switch (hbus->protocol_version) {
case PCI_PROTOCOL_VERSION_1_1:
size = hv_compose_msi_req_v1(&ctxt.int_pkts.v1,
- dest,
hpdev->desc.win_slot.slot,
(u8)vector,
vector_count);
@@ -1794,7 +1854,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
case PCI_PROTOCOL_VERSION_1_2:
case PCI_PROTOCOL_VERSION_1_3:
size = hv_compose_msi_req_v2(&ctxt.int_pkts.v2,
- dest,
+ cpu,
hpdev->desc.win_slot.slot,
(u8)vector,
vector_count);
@@ -1802,7 +1862,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
case PCI_PROTOCOL_VERSION_1_4:
size = hv_compose_msi_req_v3(&ctxt.int_pkts.v3,
- dest,
+ cpu,
hpdev->desc.win_slot.slot,
vector,
vector_count);
--
2.25.1
From: Dexuan Cui <[email protected]> Sent: Friday, November 4, 2022 3:30 PM
>
> Jeffrey added Multi-MSI support to the pci-hyperv driver by the 4 patches:
> 08e61e861a0e ("PCI: hv: Fix multi-MSI to allow more than one MSI vector")
> 455880dfe292 ("PCI: hv: Fix hv_arch_irq_unmask() for multi-MSI")
> b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> a2bad844a67b ("PCI: hv: Fix interrupt mapping for multi-MSI")
>
> It turns out that the third patch (b4b77778ecc5) causes a performance
> regression because all the interrupts now happen on 1 physical CPU (or two
> pCPUs, if one pCPU doesn't have enough vectors). When a guest has many PCI
> devices, it may suffer from soft lockups if the workload is heavy, e.g.,
> see https://lwn.net/ml/linux-kernel/[email protected]/
>
> Commit b4b77778ecc5 itself is good. The real issue is that the hypercall in
> hv_irq_unmask() -> hv_arch_irq_unmask() ->
> hv_do_hypercall(HVCALL_RETARGET_INTERRUPT...) only changes the target
> virtual CPU rather than physical CPU; with b4b77778ecc5, the pCPU is
> determined only once in hv_compose_msi_msg() where only vCPU0 is specified;
> consequently the hypervisor only uses 1 target pCPU for all the interrupts.
>
> Note: before b4b77778ecc5, the pCPU is determined twice, and when the pCPU
> is determinted the second time, the vCPU in the effective affinity mask is
> used (i.e., it isn't always vCPU0), so the hypervisor chooses different
> pCPU for each interrupt.
>
> The hypercall will be fixed in future to update the pCPU as well, but
> that will take quite a while, so let's restore the old behavior in
> hv_compose_msi_msg(), i.e., don't reuse the existing IRTE allocation for
> single-MSI and MSI-X; for multi-MSI, we choose the vCPU in a round-robin
> manner for each PCI device, so the interrupts of different devices can
> happen on different pCPUs, though the interrupts of each device happen on
> some single pCPU.
>
> The hypercall fix may not be backported to all old versions of Hyper-V, so
> we want to have this guest side change for ever (or at least till we're sure
> the old affected versions of Hyper-V are no longer supported).
>
> Fixes: b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> Co-developed-by: Jeffrey Hugo <[email protected]>
> Signed-off-by: Jeffrey Hugo <[email protected]>
> Co-developed-by: Carl Vanderlip <[email protected]>
> Signed-off-by: Carl Vanderlip <[email protected]>
> Signed-off-by: Dexuan Cui <[email protected]>
>
> ---
>
> v1 is here:
>
> https://lwn.net/ml/linux-kernel/[email protected]/
>
> Changes in v2:
> round-robin the vCPU for multi-MSI.
> The commit message is re-worked.
> Added Jeff and Carl's Co-developed-by and Signed-off-by.
>
> Changes in v3:
> Michael Kelley kindly helped to make a great comment, and I added the
> comment before hv_compose_msi_req_get_cpu(). Thank you, Michael!
>
> Rebased to Hyper-V tree's "hyperv-fixes" branch:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-fixes
>
> Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
> through the Hyper-V tree because it's rebased to another hv_pci patch (which
> only exists in the Hyper-V tree for now):
> e70af8d040d2 ("PCI: hv: Fix the definition of vector in hv_compose_msi_msg()")
>
> BTW, Michael has some other hv_pci patches, which would also need go through
> the Hyper-V tree:
>
> https://lwn.net/ml/linux-kernel/1666288635-72591-1-git-send-email-mikelley%40microsoft.com/
>
>
> drivers/pci/controller/pci-hyperv.c | 90 ++++++++++++++++++++++++-----
> 1 file changed, 75 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index ba64284eaf9f..fa5a1ba35a82 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -1613,7 +1613,7 @@ static void hv_pci_compose_compl(void *context, struct
> pci_response *resp,
> }
>
> static u32 hv_compose_msi_req_v1(
> - struct pci_create_interrupt *int_pkt, const struct cpumask *affinity,
> + struct pci_create_interrupt *int_pkt,
> u32 slot, u8 vector, u16 vector_count)
> {
> int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE;
> @@ -1631,6 +1631,35 @@ static u32 hv_compose_msi_req_v1(
> return sizeof(*int_pkt);
> }
>
> +/*
> + * The vCPU selected by hv_compose_multi_msi_req_get_cpu() and
> + * hv_compose_msi_req_get_cpu() is a "dummy" vCPU because the final vCPU to be
> + * interrupted is specified later in hv_irq_unmask() and communicated to Hyper-V
> + * via the HVCALL_RETARGET_INTERRUPT hypercall. But the choice of dummy vCPU is
> + * not irrelevant because Hyper-V chooses the physical CPU to handle the
> + * interrupts based on the vCPU specified in message sent to the vPCI VSP in
> + * hv_compose_msi_msg(). Hyper-V's choice of pCPU is not visible to the guest,
> + * but assigning too many vPCI device interrupts to the same pCPU can cause a
> + * performance bottleneck. So we spread out the dummy vCPUs to influence Hyper-
> V
> + * to spread out the pCPUs that it selects.
> + *
> + * For the single-MSI and MSI-X cases, it's OK for hv_compose_msi_req_get_cpu()
> + * to always return the same dummy vCPU, because a second call to
> + * hv_compose_msi_msg() contains the "real" vCPU, causing Hyper-V to choose a
> + * new pCPU for the interrupt. But for the multi-MSI case, the second call to
> + * hv_compose_msi_msg() exits without sending a message to the vPCI VSP, so the
> + * original dummy vCPU is used. This dummy vCPU must be round-robin'ed so that
> + * the pCPUs are spread out. All interrupts for a multi-MSI device end up using
> + * the same pCPU, even though the vCPUs will be spread out by later calls
> + * to hv_irq_unmask(), but that is the best we can do now.
> + *
> + * With current Hyper-V, the HVCALL_RETARGET_INTERRUPT hypercall does *not*
> + * cause Hyper-V to reselect the pCPU based on the specified vCPU. Such an
> + * enhancement is planned for a future version. With that enhancement, the
> + * dummy vCPU selection won't matter, and interrupts for the same multi-MSI
> + * device will be spread across multiple pCPUs.
> + */
> +
> /*
> * Create MSI w/ dummy vCPU set targeting just one vCPU, overwritten
> * by subsequent retarget in hv_irq_unmask().
> @@ -1640,18 +1669,39 @@ static int hv_compose_msi_req_get_cpu(const struct
> cpumask *affinity)
> return cpumask_first_and(affinity, cpu_online_mask);
> }
>
> -static u32 hv_compose_msi_req_v2(
> - struct pci_create_interrupt2 *int_pkt, const struct cpumask *affinity,
> - u32 slot, u8 vector, u16 vector_count)
> +/*
> + * Make sure the dummy vCPU values for multi-MSI don't all point to vCPU0.
> + */
> +static int hv_compose_multi_msi_req_get_cpu(void)
> {
> + static DEFINE_SPINLOCK(multi_msi_cpu_lock);
> +
> + /* -1 means starting with CPU 0 */
> + static int cpu_next = -1;
> +
> + unsigned long flags;
> int cpu;
>
> + spin_lock_irqsave(&multi_msi_cpu_lock, flags);
> +
> + cpu_next = cpumask_next_wrap(cpu_next, cpu_online_mask, nr_cpu_ids,
> + false);
> + cpu = cpu_next;
> +
> + spin_unlock_irqrestore(&multi_msi_cpu_lock, flags);
> +
> + return cpu;
> +}
> +
> +static u32 hv_compose_msi_req_v2(
> + struct pci_create_interrupt2 *int_pkt, int cpu,
> + u32 slot, u8 vector, u16 vector_count)
> +{
> int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE2;
> int_pkt->wslot.slot = slot;
> int_pkt->int_desc.vector = vector;
> int_pkt->int_desc.vector_count = vector_count;
> int_pkt->int_desc.delivery_mode = DELIVERY_MODE;
> - cpu = hv_compose_msi_req_get_cpu(affinity);
> int_pkt->int_desc.processor_array[0] =
> hv_cpu_number_to_vp_number(cpu);
> int_pkt->int_desc.processor_count = 1;
> @@ -1660,18 +1710,15 @@ static u32 hv_compose_msi_req_v2(
> }
>
> static u32 hv_compose_msi_req_v3(
> - struct pci_create_interrupt3 *int_pkt, const struct cpumask *affinity,
> + struct pci_create_interrupt3 *int_pkt, int cpu,
> u32 slot, u32 vector, u16 vector_count)
> {
> - int cpu;
> -
> int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE3;
> int_pkt->wslot.slot = slot;
> int_pkt->int_desc.vector = vector;
> int_pkt->int_desc.reserved = 0;
> int_pkt->int_desc.vector_count = vector_count;
> int_pkt->int_desc.delivery_mode = DELIVERY_MODE;
> - cpu = hv_compose_msi_req_get_cpu(affinity);
> int_pkt->int_desc.processor_array[0] =
> hv_cpu_number_to_vp_number(cpu);
> int_pkt->int_desc.processor_count = 1;
> @@ -1715,12 +1762,18 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
> struct pci_create_interrupt3 v3;
> } int_pkts;
> } __packed ctxt;
> + bool multi_msi;
> u64 trans_id;
> u32 size;
> int ret;
> + int cpu;
> +
> + msi_desc = irq_data_get_msi_desc(data);
> + multi_msi = !msi_desc->pci.msi_attrib.is_msix &&
> + msi_desc->nvec_used > 1;
>
> /* Reuse the previous allocation */
> - if (data->chip_data) {
> + if (data->chip_data && multi_msi) {
> int_desc = data->chip_data;
> msg->address_hi = int_desc->address >> 32;
> msg->address_lo = int_desc->address & 0xffffffff;
> @@ -1728,7 +1781,6 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
> return;
> }
>
> - msi_desc = irq_data_get_msi_desc(data);
> pdev = msi_desc_to_pci_dev(msi_desc);
> dest = irq_data_get_effective_affinity_mask(data);
> pbus = pdev->bus;
> @@ -1738,11 +1790,18 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
> if (!hpdev)
> goto return_null_message;
>
> + /* Free any previous message that might have already been composed. */
> + if (data->chip_data && !multi_msi) {
> + int_desc = data->chip_data;
> + data->chip_data = NULL;
> + hv_int_desc_free(hpdev, int_desc);
> + }
> +
> int_desc = kzalloc(sizeof(*int_desc), GFP_ATOMIC);
> if (!int_desc)
> goto drop_reference;
>
> - if (!msi_desc->pci.msi_attrib.is_msix && msi_desc->nvec_used > 1) {
> + if (multi_msi) {
> /*
> * If this is not the first MSI of Multi MSI, we already have
> * a mapping. Can exit early.
> @@ -1767,9 +1826,11 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
> */
> vector = 32;
> vector_count = msi_desc->nvec_used;
> + cpu = hv_compose_multi_msi_req_get_cpu();
> } else {
> vector = hv_msi_get_int_vector(data);
> vector_count = 1;
> + cpu = hv_compose_msi_req_get_cpu(dest);
> }
>
> /*
> @@ -1785,7 +1846,6 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
> switch (hbus->protocol_version) {
> case PCI_PROTOCOL_VERSION_1_1:
> size = hv_compose_msi_req_v1(&ctxt.int_pkts.v1,
> - dest,
> hpdev->desc.win_slot.slot,
> (u8)vector,
> vector_count);
> @@ -1794,7 +1854,7 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
> case PCI_PROTOCOL_VERSION_1_2:
> case PCI_PROTOCOL_VERSION_1_3:
> size = hv_compose_msi_req_v2(&ctxt.int_pkts.v2,
> - dest,
> + cpu,
> hpdev->desc.win_slot.slot,
> (u8)vector,
> vector_count);
> @@ -1802,7 +1862,7 @@ static void hv_compose_msi_msg(struct irq_data *data,
> struct msi_msg *msg)
>
> case PCI_PROTOCOL_VERSION_1_4:
> size = hv_compose_msi_req_v3(&ctxt.int_pkts.v3,
> - dest,
> + cpu,
> hpdev->desc.win_slot.slot,
> vector,
> vector_count);
> --
> 2.25.1
Reviewed-by: Michael Kelley <[email protected]>
> Sent: Friday, November 4, 2022 4:38 PM
> > ...
> > Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
> > through the Hyper-V tree because it's rebased to another hv_pci patch
> > (which only exists in the Hyper-V tree for now):
> > e70af8d040d2 ("PCI: hv: Fix the definition of vector in
> > hv_compose_msi_msg()")
> >
> > BTW, Michael has some other hv_pci patches, which would also need go
> > through the Hyper-V tree:
> >
> Reviewed-by: Michael Kelley <[email protected]>
Hi Bjorn, Lorenzo, if you have no objection to the patch, I suggest Wei merge
it through the Hyper-V tree early next week.
On Fri, Nov 04, 2022 at 03:29:53PM -0700, Dexuan Cui wrote:
> Jeffrey added Multi-MSI support to the pci-hyperv driver by the 4 patches:
> 08e61e861a0e ("PCI: hv: Fix multi-MSI to allow more than one MSI vector")
> 455880dfe292 ("PCI: hv: Fix hv_arch_irq_unmask() for multi-MSI")
> b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> a2bad844a67b ("PCI: hv: Fix interrupt mapping for multi-MSI")
>
> It turns out that the third patch (b4b77778ecc5) causes a performance
> regression because all the interrupts now happen on 1 physical CPU (or two
> pCPUs, if one pCPU doesn't have enough vectors). When a guest has many PCI
> devices, it may suffer from soft lockups if the workload is heavy, e.g.,
> see https://lwn.net/ml/linux-kernel/[email protected]/
>
> Commit b4b77778ecc5 itself is good. The real issue is that the hypercall in
> hv_irq_unmask() -> hv_arch_irq_unmask() ->
> hv_do_hypercall(HVCALL_RETARGET_INTERRUPT...) only changes the target
> virtual CPU rather than physical CPU; with b4b77778ecc5, the pCPU is
> determined only once in hv_compose_msi_msg() where only vCPU0 is specified;
> consequently the hypervisor only uses 1 target pCPU for all the interrupts.
>
> Note: before b4b77778ecc5, the pCPU is determined twice, and when the pCPU
> is determinted the second time, the vCPU in the effective affinity mask is
s/determinted/determined/
> used (i.e., it isn't always vCPU0), so the hypervisor chooses different
> pCPU for each interrupt.
>
> The hypercall will be fixed in future to update the pCPU as well, but
> that will take quite a while, so let's restore the old behavior in
> hv_compose_msi_msg(), i.e., don't reuse the existing IRTE allocation for
> single-MSI and MSI-X; for multi-MSI, we choose the vCPU in a round-robin
> manner for each PCI device, so the interrupts of different devices can
> happen on different pCPUs, though the interrupts of each device happen on
> some single pCPU.
>
> The hypercall fix may not be backported to all old versions of Hyper-V, so
> we want to have this guest side change for ever (or at least till we're sure
s/for ever/forever/
> the old affected versions of Hyper-V are no longer supported).
>
> Fixes: b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> Co-developed-by: Jeffrey Hugo <[email protected]>
> Signed-off-by: Jeffrey Hugo <[email protected]>
> Co-developed-by: Carl Vanderlip <[email protected]>
> Signed-off-by: Carl Vanderlip <[email protected]>
> Signed-off-by: Dexuan Cui <[email protected]>
>
> ---
>
> v1 is here:
> https://lwn.net/ml/linux-kernel/[email protected]/
>
> Changes in v2:
> round-robin the vCPU for multi-MSI.
> The commit message is re-worked.
> Added Jeff and Carl's Co-developed-by and Signed-off-by.
>
> Changes in v3:
> Michael Kelley kindly helped to make a great comment, and I added the
> comment before hv_compose_msi_req_get_cpu(). Thank you, Michael!
>
> Rebased to Hyper-V tree's "hyperv-fixes" branch:
> https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-fixes
>
> Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
> through the Hyper-V tree because it's rebased to another hv_pci patch (which
> only exists in the Hyper-V tree for now):
> e70af8d040d2 ("PCI: hv: Fix the definition of vector in hv_compose_msi_msg()")
Fine with me, but it's Lorenzo's area so I don't want to preemptively
ack it.
> From: Bjorn Helgaas <[email protected]>
> Sent: Thursday, November 10, 2022 1:44 PM
> > ...
> > Note: before b4b77778ecc5, the pCPU is determined twice, and when the
> > pCPU is determinted the second time, the vCPU in the effective affinity
> > mask is
>
> s/determinted/determined/
Thanks, Bjorn! I suppose Wei can help fix this :-)
> > The hypercall fix may not be backported to all old versions of Hyper-V, so
> > we want to have this guest side change for ever (or at least till we're sure
>
> s/for ever/forever/
ditto.
> > Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
> > through the Hyper-V tree because it's rebased to another hv_pci patch
> > (which only exists in the Hyper-V tree for now):
> > e70af8d040d2 ("PCI: hv: Fix the definition of vector in
> > hv_compose_msi_msg()")
>
> Fine with me, but it's Lorenzo's area so I don't want to preemptively
> ack it.
Thanks. Hopefully Lorenzo can take a look soon.
On Fri, Nov 04, 2022 at 03:29:53PM -0700, Dexuan Cui wrote:
> Jeffrey added Multi-MSI support to the pci-hyperv driver by the 4 patches:
> 08e61e861a0e ("PCI: hv: Fix multi-MSI to allow more than one MSI vector")
> 455880dfe292 ("PCI: hv: Fix hv_arch_irq_unmask() for multi-MSI")
> b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> a2bad844a67b ("PCI: hv: Fix interrupt mapping for multi-MSI")
>
> It turns out that the third patch (b4b77778ecc5) causes a performance
> regression because all the interrupts now happen on 1 physical CPU (or two
> pCPUs, if one pCPU doesn't have enough vectors). When a guest has many PCI
> devices, it may suffer from soft lockups if the workload is heavy, e.g.,
> see https://lwn.net/ml/linux-kernel/[email protected]/
>
> Commit b4b77778ecc5 itself is good. The real issue is that the hypercall in
> hv_irq_unmask() -> hv_arch_irq_unmask() ->
> hv_do_hypercall(HVCALL_RETARGET_INTERRUPT...) only changes the target
> virtual CPU rather than physical CPU; with b4b77778ecc5, the pCPU is
> determined only once in hv_compose_msi_msg() where only vCPU0 is specified;
> consequently the hypervisor only uses 1 target pCPU for all the interrupts.
>
> Note: before b4b77778ecc5, the pCPU is determined twice, and when the pCPU
> is determinted the second time, the vCPU in the effective affinity mask is
> used (i.e., it isn't always vCPU0), so the hypervisor chooses different
> pCPU for each interrupt.
>
> The hypercall will be fixed in future to update the pCPU as well, but
> that will take quite a while, so let's restore the old behavior in
> hv_compose_msi_msg(), i.e., don't reuse the existing IRTE allocation for
> single-MSI and MSI-X; for multi-MSI, we choose the vCPU in a round-robin
> manner for each PCI device, so the interrupts of different devices can
> happen on different pCPUs, though the interrupts of each device happen on
> some single pCPU.
>
> The hypercall fix may not be backported to all old versions of Hyper-V, so
> we want to have this guest side change for ever (or at least till we're sure
> the old affected versions of Hyper-V are no longer supported).
>
> Fixes: b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> Co-developed-by: Jeffrey Hugo <[email protected]>
> Signed-off-by: Jeffrey Hugo <[email protected]>
> Co-developed-by: Carl Vanderlip <[email protected]>
> Signed-off-by: Carl Vanderlip <[email protected]>
> Signed-off-by: Dexuan Cui <[email protected]>
>
> ---
>
> v1 is here:
> https://lwn.net/ml/linux-kernel/[email protected]/
>
> Changes in v2:
> round-robin the vCPU for multi-MSI.
> The commit message is re-worked.
> Added Jeff and Carl's Co-developed-by and Signed-off-by.
>
> Changes in v3:
> Michael Kelley kindly helped to make a great comment, and I added the
> comment before hv_compose_msi_req_get_cpu(). Thank you, Michael!
>
> Rebased to Hyper-V tree's "hyperv-fixes" branch:
> https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-fixes
>
> Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
> through the Hyper-V tree because it's rebased to another hv_pci patch (which
> only exists in the Hyper-V tree for now):
> e70af8d040d2 ("PCI: hv: Fix the definition of vector in hv_compose_msi_msg()")
>
> BTW, Michael has some other hv_pci patches, which would also need go through
> the Hyper-V tree:
> https://lwn.net/ml/linux-kernel/1666288635-72591-1-git-send-email-mikelley%40microsoft.com/
>
>
> drivers/pci/controller/pci-hyperv.c | 90 ++++++++++++++++++++++++-----
> 1 file changed, 75 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index ba64284eaf9f..fa5a1ba35a82 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -1613,7 +1613,7 @@ static void hv_pci_compose_compl(void *context, struct pci_response *resp,
> }
>
> static u32 hv_compose_msi_req_v1(
> - struct pci_create_interrupt *int_pkt, const struct cpumask *affinity,
> + struct pci_create_interrupt *int_pkt,
> u32 slot, u8 vector, u16 vector_count)
> {
> int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE;
> @@ -1631,6 +1631,35 @@ static u32 hv_compose_msi_req_v1(
> return sizeof(*int_pkt);
> }
>
> +/*
> + * The vCPU selected by hv_compose_multi_msi_req_get_cpu() and
> + * hv_compose_msi_req_get_cpu() is a "dummy" vCPU because the final vCPU to be
> + * interrupted is specified later in hv_irq_unmask() and communicated to Hyper-V
> + * via the HVCALL_RETARGET_INTERRUPT hypercall. But the choice of dummy vCPU is
> + * not irrelevant because Hyper-V chooses the physical CPU to handle the
> + * interrupts based on the vCPU specified in message sent to the vPCI VSP in
> + * hv_compose_msi_msg(). Hyper-V's choice of pCPU is not visible to the guest,
> + * but assigning too many vPCI device interrupts to the same pCPU can cause a
> + * performance bottleneck. So we spread out the dummy vCPUs to influence Hyper-V
> + * to spread out the pCPUs that it selects.
> + *
> + * For the single-MSI and MSI-X cases, it's OK for hv_compose_msi_req_get_cpu()
> + * to always return the same dummy vCPU, because a second call to
> + * hv_compose_msi_msg() contains the "real" vCPU, causing Hyper-V to choose a
> + * new pCPU for the interrupt. But for the multi-MSI case, the second call to
> + * hv_compose_msi_msg() exits without sending a message to the vPCI VSP, so the
Why ? Can't you fix _that_ ? Why can't the initial call to
hv_compose_msi_msg() determine the _real_ target vCPU ?
> + * original dummy vCPU is used. This dummy vCPU must be round-robin'ed so that
> + * the pCPUs are spread out. All interrupts for a multi-MSI device end up using
> + * the same pCPU, even though the vCPUs will be spread out by later calls
> + * to hv_irq_unmask(), but that is the best we can do now.
> + *
> + * With current Hyper-V, the HVCALL_RETARGET_INTERRUPT hypercall does *not*
"current" Hyper-V means nothing, remove it or provide versioning
information. Imagine yourself reading this comment some time
in the future.
I can't claim to understand how this MSI vCPU to pCPU mapping is made to
work in current code but I can't ack this patch sorry, if you feel like
it is good to merge it it is your and Hyper-V maintainers call, feel
free to go ahead - I can review PCI hyper-V changes that affect PCI
and IRQs core APIs, I don't know Hyper-V internals.
Lorenzo
> + * cause Hyper-V to reselect the pCPU based on the specified vCPU. Such an
> + * enhancement is planned for a future version. With that enhancement, the
> + * dummy vCPU selection won't matter, and interrupts for the same multi-MSI
> + * device will be spread across multiple pCPUs.
> + */
> +
> /*
> * Create MSI w/ dummy vCPU set targeting just one vCPU, overwritten
> * by subsequent retarget in hv_irq_unmask().
> @@ -1640,18 +1669,39 @@ static int hv_compose_msi_req_get_cpu(const struct cpumask *affinity)
> return cpumask_first_and(affinity, cpu_online_mask);
> }
>
> -static u32 hv_compose_msi_req_v2(
> - struct pci_create_interrupt2 *int_pkt, const struct cpumask *affinity,
> - u32 slot, u8 vector, u16 vector_count)
> +/*
> + * Make sure the dummy vCPU values for multi-MSI don't all point to vCPU0.
> + */
> +static int hv_compose_multi_msi_req_get_cpu(void)
> {
> + static DEFINE_SPINLOCK(multi_msi_cpu_lock);
> +
> + /* -1 means starting with CPU 0 */
> + static int cpu_next = -1;
> +
> + unsigned long flags;
> int cpu;
>
> + spin_lock_irqsave(&multi_msi_cpu_lock, flags);
> +
> + cpu_next = cpumask_next_wrap(cpu_next, cpu_online_mask, nr_cpu_ids,
> + false);
> + cpu = cpu_next;
> +
> + spin_unlock_irqrestore(&multi_msi_cpu_lock, flags);
> +
> + return cpu;
> +}
> +
> +static u32 hv_compose_msi_req_v2(
> + struct pci_create_interrupt2 *int_pkt, int cpu,
> + u32 slot, u8 vector, u16 vector_count)
> +{
> int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE2;
> int_pkt->wslot.slot = slot;
> int_pkt->int_desc.vector = vector;
> int_pkt->int_desc.vector_count = vector_count;
> int_pkt->int_desc.delivery_mode = DELIVERY_MODE;
> - cpu = hv_compose_msi_req_get_cpu(affinity);
> int_pkt->int_desc.processor_array[0] =
> hv_cpu_number_to_vp_number(cpu);
> int_pkt->int_desc.processor_count = 1;
> @@ -1660,18 +1710,15 @@ static u32 hv_compose_msi_req_v2(
> }
>
> static u32 hv_compose_msi_req_v3(
> - struct pci_create_interrupt3 *int_pkt, const struct cpumask *affinity,
> + struct pci_create_interrupt3 *int_pkt, int cpu,
> u32 slot, u32 vector, u16 vector_count)
> {
> - int cpu;
> -
> int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE3;
> int_pkt->wslot.slot = slot;
> int_pkt->int_desc.vector = vector;
> int_pkt->int_desc.reserved = 0;
> int_pkt->int_desc.vector_count = vector_count;
> int_pkt->int_desc.delivery_mode = DELIVERY_MODE;
> - cpu = hv_compose_msi_req_get_cpu(affinity);
> int_pkt->int_desc.processor_array[0] =
> hv_cpu_number_to_vp_number(cpu);
> int_pkt->int_desc.processor_count = 1;
> @@ -1715,12 +1762,18 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> struct pci_create_interrupt3 v3;
> } int_pkts;
> } __packed ctxt;
> + bool multi_msi;
> u64 trans_id;
> u32 size;
> int ret;
> + int cpu;
> +
> + msi_desc = irq_data_get_msi_desc(data);
> + multi_msi = !msi_desc->pci.msi_attrib.is_msix &&
> + msi_desc->nvec_used > 1;
>
> /* Reuse the previous allocation */
> - if (data->chip_data) {
> + if (data->chip_data && multi_msi) {
> int_desc = data->chip_data;
> msg->address_hi = int_desc->address >> 32;
> msg->address_lo = int_desc->address & 0xffffffff;
> @@ -1728,7 +1781,6 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> return;
> }
>
> - msi_desc = irq_data_get_msi_desc(data);
> pdev = msi_desc_to_pci_dev(msi_desc);
> dest = irq_data_get_effective_affinity_mask(data);
> pbus = pdev->bus;
> @@ -1738,11 +1790,18 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> if (!hpdev)
> goto return_null_message;
>
> + /* Free any previous message that might have already been composed. */
> + if (data->chip_data && !multi_msi) {
> + int_desc = data->chip_data;
> + data->chip_data = NULL;
> + hv_int_desc_free(hpdev, int_desc);
> + }
> +
> int_desc = kzalloc(sizeof(*int_desc), GFP_ATOMIC);
> if (!int_desc)
> goto drop_reference;
>
> - if (!msi_desc->pci.msi_attrib.is_msix && msi_desc->nvec_used > 1) {
> + if (multi_msi) {
> /*
> * If this is not the first MSI of Multi MSI, we already have
> * a mapping. Can exit early.
> @@ -1767,9 +1826,11 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> */
> vector = 32;
> vector_count = msi_desc->nvec_used;
> + cpu = hv_compose_multi_msi_req_get_cpu();
> } else {
> vector = hv_msi_get_int_vector(data);
> vector_count = 1;
> + cpu = hv_compose_msi_req_get_cpu(dest);
> }
>
> /*
> @@ -1785,7 +1846,6 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> switch (hbus->protocol_version) {
> case PCI_PROTOCOL_VERSION_1_1:
> size = hv_compose_msi_req_v1(&ctxt.int_pkts.v1,
> - dest,
> hpdev->desc.win_slot.slot,
> (u8)vector,
> vector_count);
> @@ -1794,7 +1854,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> case PCI_PROTOCOL_VERSION_1_2:
> case PCI_PROTOCOL_VERSION_1_3:
> size = hv_compose_msi_req_v2(&ctxt.int_pkts.v2,
> - dest,
> + cpu,
> hpdev->desc.win_slot.slot,
> (u8)vector,
> vector_count);
> @@ -1802,7 +1862,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>
> case PCI_PROTOCOL_VERSION_1_4:
> size = hv_compose_msi_req_v3(&ctxt.int_pkts.v3,
> - dest,
> + cpu,
> hpdev->desc.win_slot.slot,
> vector,
> vector_count);
> --
> 2.25.1
>
On Fri, Nov 11, 2022 at 10:56:28AM +0100, Lorenzo Pieralisi wrote:
> On Fri, Nov 04, 2022 at 03:29:53PM -0700, Dexuan Cui wrote:
> > Jeffrey added Multi-MSI support to the pci-hyperv driver by the 4 patches:
> > 08e61e861a0e ("PCI: hv: Fix multi-MSI to allow more than one MSI vector")
> > 455880dfe292 ("PCI: hv: Fix hv_arch_irq_unmask() for multi-MSI")
> > b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> > a2bad844a67b ("PCI: hv: Fix interrupt mapping for multi-MSI")
> >
> > It turns out that the third patch (b4b77778ecc5) causes a performance
> > regression because all the interrupts now happen on 1 physical CPU (or two
> > pCPUs, if one pCPU doesn't have enough vectors). When a guest has many PCI
> > devices, it may suffer from soft lockups if the workload is heavy, e.g.,
> > see https://lwn.net/ml/linux-kernel/[email protected]/
> >
> > Commit b4b77778ecc5 itself is good. The real issue is that the hypercall in
> > hv_irq_unmask() -> hv_arch_irq_unmask() ->
> > hv_do_hypercall(HVCALL_RETARGET_INTERRUPT...) only changes the target
> > virtual CPU rather than physical CPU; with b4b77778ecc5, the pCPU is
> > determined only once in hv_compose_msi_msg() where only vCPU0 is specified;
> > consequently the hypervisor only uses 1 target pCPU for all the interrupts.
> >
> > Note: before b4b77778ecc5, the pCPU is determined twice, and when the pCPU
> > is determinted the second time, the vCPU in the effective affinity mask is
> > used (i.e., it isn't always vCPU0), so the hypervisor chooses different
> > pCPU for each interrupt.
> >
> > The hypercall will be fixed in future to update the pCPU as well, but
> > that will take quite a while, so let's restore the old behavior in
> > hv_compose_msi_msg(), i.e., don't reuse the existing IRTE allocation for
> > single-MSI and MSI-X; for multi-MSI, we choose the vCPU in a round-robin
> > manner for each PCI device, so the interrupts of different devices can
> > happen on different pCPUs, though the interrupts of each device happen on
> > some single pCPU.
> >
> > The hypercall fix may not be backported to all old versions of Hyper-V, so
> > we want to have this guest side change for ever (or at least till we're sure
> > the old affected versions of Hyper-V are no longer supported).
> >
> > Fixes: b4b77778ecc5 ("PCI: hv: Reuse existing IRTE allocation in compose_msi_msg()")
> > Co-developed-by: Jeffrey Hugo <[email protected]>
> > Signed-off-by: Jeffrey Hugo <[email protected]>
> > Co-developed-by: Carl Vanderlip <[email protected]>
> > Signed-off-by: Carl Vanderlip <[email protected]>
> > Signed-off-by: Dexuan Cui <[email protected]>
> >
> > ---
> >
> > v1 is here:
> > https://lwn.net/ml/linux-kernel/[email protected]/
> >
> > Changes in v2:
> > round-robin the vCPU for multi-MSI.
> > The commit message is re-worked.
> > Added Jeff and Carl's Co-developed-by and Signed-off-by.
> >
> > Changes in v3:
> > Michael Kelley kindly helped to make a great comment, and I added the
> > comment before hv_compose_msi_req_get_cpu(). Thank you, Michael!
> >
> > Rebased to Hyper-V tree's "hyperv-fixes" branch:
> > https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-fixes
> >
> > Bjorn, Lorenzo, it would be great to have your Ack. The patch needs to go
> > through the Hyper-V tree because it's rebased to another hv_pci patch (which
> > only exists in the Hyper-V tree for now):
> > e70af8d040d2 ("PCI: hv: Fix the definition of vector in hv_compose_msi_msg()")
> >
> > BTW, Michael has some other hv_pci patches, which would also need go through
> > the Hyper-V tree:
> > https://lwn.net/ml/linux-kernel/1666288635-72591-1-git-send-email-mikelley%40microsoft.com/
> >
> >
> > drivers/pci/controller/pci-hyperv.c | 90 ++++++++++++++++++++++++-----
> > 1 file changed, 75 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index ba64284eaf9f..fa5a1ba35a82 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -1613,7 +1613,7 @@ static void hv_pci_compose_compl(void *context, struct pci_response *resp,
> > }
> >
> > static u32 hv_compose_msi_req_v1(
> > - struct pci_create_interrupt *int_pkt, const struct cpumask *affinity,
> > + struct pci_create_interrupt *int_pkt,
> > u32 slot, u8 vector, u16 vector_count)
> > {
> > int_pkt->message_type.type = PCI_CREATE_INTERRUPT_MESSAGE;
> > @@ -1631,6 +1631,35 @@ static u32 hv_compose_msi_req_v1(
> > return sizeof(*int_pkt);
> > }
> >
> > +/*
> > + * The vCPU selected by hv_compose_multi_msi_req_get_cpu() and
> > + * hv_compose_msi_req_get_cpu() is a "dummy" vCPU because the final vCPU to be
> > + * interrupted is specified later in hv_irq_unmask() and communicated to Hyper-V
> > + * via the HVCALL_RETARGET_INTERRUPT hypercall. But the choice of dummy vCPU is
> > + * not irrelevant because Hyper-V chooses the physical CPU to handle the
> > + * interrupts based on the vCPU specified in message sent to the vPCI VSP in
> > + * hv_compose_msi_msg(). Hyper-V's choice of pCPU is not visible to the guest,
> > + * but assigning too many vPCI device interrupts to the same pCPU can cause a
> > + * performance bottleneck. So we spread out the dummy vCPUs to influence Hyper-V
> > + * to spread out the pCPUs that it selects.
> > + *
> > + * For the single-MSI and MSI-X cases, it's OK for hv_compose_msi_req_get_cpu()
> > + * to always return the same dummy vCPU, because a second call to
> > + * hv_compose_msi_msg() contains the "real" vCPU, causing Hyper-V to choose a
> > + * new pCPU for the interrupt. But for the multi-MSI case, the second call to
> > + * hv_compose_msi_msg() exits without sending a message to the vPCI VSP, so the
>
> Why ? Can't you fix _that_ ? Why can't the initial call to
> hv_compose_msi_msg() determine the _real_ target vCPU ?
Dexuan, any comment on this?
>
> > + * original dummy vCPU is used. This dummy vCPU must be round-robin'ed so that
> > + * the pCPUs are spread out. All interrupts for a multi-MSI device end up using
> > + * the same pCPU, even though the vCPUs will be spread out by later calls
> > + * to hv_irq_unmask(), but that is the best we can do now.
> > + *
> > + * With current Hyper-V, the HVCALL_RETARGET_INTERRUPT hypercall does *not*
>
> "current" Hyper-V means nothing, remove it or provide versioning
> information. Imagine yourself reading this comment some time
> in the future.
>
And this?
Wei.
> From: Lorenzo Pieralisi <[email protected]>
> Sent: Friday, November 11, 2022 1:56 AM
> > ...
> > + * For the single-MSI and MSI-X cases, it's OK for
> > hv_compose_msi_req_get_cpu()
> > + * to always return the same dummy vCPU, because a second call to
> > + * hv_compose_msi_msg() contains the "real" vCPU, causing Hyper-V to
> > choose a
> > + * new pCPU for the interrupt. But for the multi-MSI case, the second call to
> > + * hv_compose_msi_msg() exits without sending a message to the vPCI VSP,
> > so the
>
> Why ? Can't you fix _that_ ? Why can't the initial call to
> hv_compose_msi_msg() determine the _real_ target vCPU ?
Unluckily I can't fix this because of the way it works in x86's irq management
code. This is out of the control of the pci-hyperv driver.
hv_compose_msi_msg() uses irq_data_get_effective_affinity_mask() to get
the "effective"mask.
On x86, when the irq is initialized, irq_data_update_effective_affinity() is
called from apic_update_irq_cfg() -- please refer to the below debug code.
When the initial call to hv_compose_msi_msg() is invoked, it's from
pci_alloc_irq_vectors(), and the x86 irq code always passes CPU0 to pci-hyperv.
Please see the below "cpumask_first(cpu_online_mask)" in
vector_assign_managed_shutdown().
When hv_compose_msi_msg() is invoked the second time, it's from
request_irq(), and the x86 irq code passes the real effectivey CPU to pci-hyperv.
I added the below debug code and pasted the trimmed output below.
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -179,6 +179,7 @@ static void vector_assign_managed_shutdown(struct irq_data *irqd)
unsigned int cpu = cpumask_first(cpu_online_mask);
apic_update_irq_cfg(irqd, MANAGED_IRQ_SHUTDOWN_VECTOR, cpu);
+ WARN(irqd->irq >= 24, "cdx: vector_assign_managed_shutdown: irq=%d, cpu=%d\n", irqd->irq, cpu);
}
static int reserve_managed_vector(struct irq_data *irqd)
@@ -251,6 +252,7 @@ assign_vector_locked(struct irq_data *irqd, const struct cpumask *dest)
return vector;
apic_update_vector(irqd, vector, cpu);
apic_update_irq_cfg(irqd, vector, cpu);
+ WARN(irqd->irq >= 24, "cdx: assign_vector_locked: irq=%d, cpu=%d\n", irqd->irq, cpu);
return 0;
}
@@ -328,6 +330,7 @@ assign_managed_vector(struct irq_data *irqd, const struct cpumask *dest)
return vector;
apic_update_vector(irqd, vector, cpu);
apic_update_irq_cfg(irqd, vector, cpu);
+ WARN(irqd->irq >= 24, "cdx: assign_managed_vector: irq=%d, cpu=%d\n", irqd->irq, cpu);
return 0;
}
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -1803,6 +1803,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
u32 size;
int ret;
+ WARN(1, "cdx: hv_compose_msi_msg: irq=%d\n", data->irq);
/* Reuse the previous allocation */
if (data->chip_data) {
int_desc = data->chip_data;
1 cdx: vector_assign_managed_shutdown: irq=24, cpu=0
2 WARNING: CPU: 3 PID: 87 at arch/x86/kernel/apic/vector.c:182 vector_assign_managed_shutdown+0x53/0x60
3 RIP: 0010:vector_assign_managed_shutdown+0x53/0x60
4 reserve_irq_vector_locked+0x41/0xa0
5 x86_vector_alloc_irqs+0x298/0x460
6 irq_domain_alloc_irqs_hierarchy+0x1b/0x50
7 irq_domain_alloc_irqs_parent+0x17/0x30
8 msi_domain_alloc+0x83/0x150
9 irq_domain_alloc_irqs_hierarchy+0x1b/0x50
10 __irq_domain_alloc_irqs+0xdf/0x320
11 __msi_domain_alloc_irqs+0x103/0x3e0
12 msi_domain_alloc_irqs_descs_locked+0x3e/0x90
13 pci_msi_setup_msi_irqs+0x2d/0x40
14 __pci_enable_msix_range+0x2fd/0x420
15 pci_alloc_irq_vectors_affinity+0xb0/0x110
16 nvme_reset_work+0x1cf/0x1170
17 process_one_work+0x21f/0x3f0
18 worker_thread+0x4a/0x3c0
19 kthread+0xff/0x130
20 ret_from_fork+0x22/0x30
21
22 cdx: vector_assign_managed_shutdown: irq=24, cpu=0
23 WARNING: CPU: 3 PID: 87 at arch/x86/kernel/apic/vector.c:182 vector_assign_managed_shutdown+0x53/0x60
24 RIP: 0010:vector_assign_managed_shutdown+0x53/0x60
25 x86_vector_activate+0x149/0x1e0
26 __irq_domain_activate_irq+0x58/0x90
27 __irq_domain_activate_irq+0x38/0x90
28 irq_domain_activate_irq+0x2d/0x50
29 __msi_domain_alloc_irqs+0x1bb/0x3e0
30 msi_domain_alloc_irqs_descs_locked+0x3e/0x90
31 pci_msi_setup_msi_irqs+0x2d/0x40
32 __pci_enable_msix_range+0x2fd/0x420
33 pci_alloc_irq_vectors_affinity+0xb0/0x110
34 nvme_reset_work+0x1cf/0x1170
35 process_one_work+0x21f/0x3f0
36 worker_thread+0x4a/0x3c0
37 kthread+0xff/0x130
38 ret_from_fork+0x22/0x30
39
40
41 cdx: hv_compose_msi_msg: irq=24
42 WARNING: CPU: 3 PID: 87 at drivers/pci/controller/pci-hyperv.c:1806 hv_compose_msi_msg+0x3f/0x5d0 [pci_hyperv]
43 RIP: 0010:hv_compose_msi_msg+0x3f/0x5d0 [pci_hyperv]
44 irq_chip_compose_msi_msg+0x32/0x50
45 msi_domain_activate+0x45/0xa0
46 __irq_domain_activate_irq+0x58/0x90
47 irq_domain_activate_irq+0x2d/0x50
48 __msi_domain_alloc_irqs+0x1bb/0x3e0
49 msi_domain_alloc_irqs_descs_locked+0x3e/0x90
50 pci_msi_setup_msi_irqs+0x2d/0x40
51 __pci_enable_msix_range+0x2fd/0x420
52 pci_alloc_irq_vectors_affinity+0xb0/0x110
53 nvme_reset_work+0x1cf/0x1170
54 process_one_work+0x21f/0x3f0
55 worker_thread+0x4a/0x3c0
56 kthread+0xff/0x130
57 ret_from_fork+0x22/0x30
58
59
60
61 cdx: assign_vector_locked: irq=24, cpu=3
62 WARNING: CPU: 0 PID: 87 at arch/x86/kernel/apic/vector.c:255 assign_vector_locked+0x160/0x170
63 RIP: 0010:assign_vector_locked+0x160/0x170
64 assign_irq_vector_any_locked+0x6a/0x150
65 x86_vector_activate+0x93/0x1e0
66 __irq_domain_activate_irq+0x58/0x90
67 __irq_domain_activate_irq+0x38/0x90
68 irq_domain_activate_irq+0x2d/0x50
69 irq_activate+0x29/0x30
70 __setup_irq+0x2e5/0x780
71 request_threaded_irq+0x112/0x180
72 pci_request_irq+0xa3/0xf0
73 queue_request_irq+0x74/0x80
74 nvme_reset_work+0x408/0x1170
75 process_one_work+0x21f/0x3f0
76 worker_thread+0x4a/0x3c0
77 kthread+0xff/0x130
78 ret_from_fork+0x22/0x30
79
80 cdx: hv_compose_msi_msg: irq=24
81 WARNING: CPU: 0 PID: 87 at drivers/pci/controller/pci-hyperv.c:1806 hv_compose_msi_msg+0x3f/0x5d0 [pci_hyperv]
82 RIP: 0010:hv_compose_msi_msg+0x3f/0x5d0 [pci_hyperv]
83 irq_chip_compose_msi_msg+0x32/0x50
84 msi_domain_activate+0x45/0xa0
85 __irq_domain_activate_irq+0x58/0x90
86 irq_domain_activate_irq+0x2d/0x50
87 irq_activate+0x29/0x30
88 __setup_irq+0x2e5/0x780
89 request_threaded_irq+0x112/0x180
90 pci_request_irq+0xa3/0xf0
91 queue_request_irq+0x74/0x80
92 nvme_reset_work+0x408/0x1170
93 process_one_work+0x21f/0x3f0
94 worker_thread+0x4a/0x3c0
95 kthread+0xff/0x130
96 ret_from_fork+0x22/0x30
> > + * original dummy vCPU is used. This dummy vCPU must be round-robin'ed
> > so that
> > + * the pCPUs are spread out. All interrupts for a multi-MSI device end up
> > using
> > + * the same pCPU, even though the vCPUs will be spread out by later calls
> > + * to hv_irq_unmask(), but that is the best we can do now.
> > + *
> > + * With current Hyper-V, the HVCALL_RETARGET_INTERRUPT hypercall does
> *not*
>
> "current" Hyper-V means nothing, remove it or provide versioning
> information. Imagine yourself reading this comment some time
> in the future.
Good point. @Wei, can you please help fix this? I think we can change
"With current Hyper-V"
To
"With Hyper-V in Nov 2022".
BTW, it's hard to provide the exact versioning info, because technically
there are many versions of Hyper-V...
> I can't claim to understand how this MSI vCPU to pCPU mapping is made to
> work in current code but I can't ack this patch sorry, if you feel like
> it is good to merge it it is your and Hyper-V maintainers call, feel
> free to go ahead - I can review PCI hyper-V changes that affect PCI
> and IRQs core APIs, I don't know Hyper-V internals.
>
> Lorenzo
I understand. Thanks!
I discussed the issue with Hyper-V team. I believe I understood it and
this patch is the right thing to have.
@Wei, Bjorn spotted two typos in the commit message, and Lorenzo
suggested a change to the above "current". Can you please help
fix these and merge the patch? Or, let me know if it'd be easier if
I should send v4.
Thanks,
Dexuan
On Sat, Nov 12, 2022 at 12:58:33AM +0000, Dexuan Cui wrote:
[...]
>
> I discussed the issue with Hyper-V team. I believe I understood it and
> this patch is the right thing to have.
>
> @Wei, Bjorn spotted two typos in the commit message, and Lorenzo
> suggested a change to the above "current". Can you please help
> fix these and merge the patch? Or, let me know if it'd be easier if
> I should send v4.
All fixed and patch applied to hyperv-fixes.
Thanks,
Wei.
>
> Thanks,
> Dexuan
>