This series tries to add basic busy polling for vhost net. The idea is
simple: at the end of tx/rx processing, busy polling for new tx added
descriptor and rx receive socket for a while. The maximum number of
time (in us) could be spent on busy polling was specified ioctl.
Test A were done through:
- 50 us as busy loop timeout
- Netperf 2.6
- Two machines with back to back connected mlx4
- Guest with 1 vcpus and 1 queue
Results:
- Obvious improvements (%5 - 20%) for latency (TCP_RR).
- Get a better or minor regression on most of the TX tests, but see
some regression on 4096 size.
- Except for 8 sessions of 4096 size RX, have a better or same
performance.
- CPU utilization were incrased as expected.
TCP_RR:
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
1/ 1/ +8%/ -32%/ +8%/ +8%/ +7%
1/ 50/ +7%/ -19%/ +7%/ +7%/ +1%
1/ 100/ +5%/ -21%/ +5%/ +5%/ 0%
1/ 200/ +5%/ -21%/ +7%/ +7%/ +1%
64/ 1/ +11%/ -29%/ +11%/ +11%/ +10%
64/ 50/ +7%/ -19%/ +8%/ +8%/ +2%
64/ 100/ +8%/ -18%/ +9%/ +9%/ +2%
64/ 200/ +6%/ -19%/ +6%/ +6%/ 0%
256/ 1/ +7%/ -33%/ +7%/ +7%/ +6%
256/ 50/ +7%/ -18%/ +7%/ +7%/ 0%
256/ 100/ +9%/ -18%/ +8%/ +8%/ +2%
256/ 200/ +9%/ -18%/ +10%/ +10%/ +3%
1024/ 1/ +20%/ -28%/ +20%/ +20%/ +19%
1024/ 50/ +8%/ -18%/ +9%/ +9%/ +2%
1024/ 100/ +6%/ -19%/ +5%/ +5%/ 0%
1024/ 200/ +8%/ -18%/ +9%/ +9%/ +2%
Guest TX:
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
64/ 1/ -5%/ -28%/ +11%/ +12%/ +10%
64/ 4/ -2%/ -26%/ +13%/ +13%/ +13%
64/ 8/ -6%/ -29%/ +9%/ +10%/ +10%
512/ 1/ +15%/ -7%/ +13%/ +11%/ +3%
512/ 4/ +17%/ -6%/ +18%/ +13%/ +11%
512/ 8/ +14%/ -7%/ +13%/ +7%/ +7%
1024/ 1/ +27%/ -2%/ +26%/ +29%/ +12%
1024/ 4/ +8%/ -9%/ +6%/ +1%/ +6%
1024/ 8/ +41%/ +12%/ +34%/ +20%/ -3%
4096/ 1/ -22%/ -21%/ -36%/ +81%/+1360%
4096/ 4/ -57%/ -58%/ +286%/ +15%/+2074%
4096/ 8/ +67%/ +70%/ -45%/ -8%/ +63%
16384/ 1/ -2%/ -5%/ +5%/ -3%/ +80%
16384/ 4/ 0%/ 0%/ 0%/ +4%/ +138%
16384/ 8/ 0%/ 0%/ 0%/ +1%/ +41%
65535/ 1/ -3%/ -6%/ +2%/ +11%/ +113%
65535/ 4/ -2%/ -1%/ -2%/ -3%/ +484%
65535/ 8/ 0%/ +1%/ 0%/ +2%/ +40%
Guest RX:
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
64/ 1/ +31%/ -3%/ +8%/ +8%/ +8%
64/ 4/ +11%/ -17%/ +13%/ +14%/ +15%
64/ 8/ +4%/ -23%/ +11%/ +11%/ +12%
512/ 1/ +24%/ 0%/ +18%/ +14%/ -8%
512/ 4/ +4%/ -15%/ +6%/ +5%/ +6%
512/ 8/ +26%/ 0%/ +21%/ +10%/ +3%
1024/ 1/ +88%/ +47%/ +69%/ +44%/ -30%
1024/ 4/ +18%/ -5%/ +19%/ +16%/ +2%
1024/ 8/ +15%/ -4%/ +13%/ +8%/ +1%
4096/ 1/ -3%/ -5%/ +2%/ -2%/ +41%
4096/ 4/ +2%/ +3%/ -20%/ -14%/ -24%
4096/ 8/ -43%/ -45%/ +69%/ -24%/ +94%
16384/ 1/ -3%/ -11%/ +23%/ +7%/ +42%
16384/ 4/ -3%/ -3%/ -4%/ +5%/ +115%
16384/ 8/ -1%/ 0%/ -1%/ -3%/ +32%
65535/ 1/ +1%/ 0%/ +2%/ 0%/ +66%
65535/ 4/ -1%/ -1%/ 0%/ +4%/ +492%
65535/ 8/ 0%/ -1%/ -1%/ +4%/ +38%
Changes from V3:
- drop single_task_running()
- use cpu_relax_lowlatency() instead of cpu_relax()
Changes from V2:
- rename vhost_vq_more_avail() to vhost_vq_avail_empty(). And return
false we __get_user() fails.
- do not bother premmptions/timers for good path.
- use vhost_vring_state as ioctl parameter instead of reinveting a new
one.
- add the unit of timeout (us) to the comment of new added ioctls
Changes from V1:
- remove the buggy vq_error() in vhost_vq_more_avail().
- leave vhost_enable_notify() untouched.
Changes from RFC V3:
- small tweak on the code to avoid multiple duplicate conditions in
critical path when busy loop is not enabled.
- add the test result of multiple VMs
Changes from RFC V2:
- poll also at the end of rx handling
- factor out the polling logic and optimize the code a little bit
- add two ioctls to get and set the busy poll timeout
- test on ixgbe (which can give more stable and reproducable numbers)
instead of mlx4.
Changes from RFC V1:
- add a comment for vhost_has_work() to explain why it could be
lockless
- add param description for busyloop_timeout
- split out the busy polling logic into a new helper
- check and exit the loop when there's a pending signal
- disable preemption during busy looping to make sure lock_clock() was
correctly used.
Jason Wang (3):
vhost: introduce vhost_has_work()
vhost: introduce vhost_vq_avail_empty()
vhost_net: basic polling support
drivers/vhost/net.c | 78 +++++++++++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.c | 35 +++++++++++++++++++++
drivers/vhost/vhost.h | 3 ++
include/uapi/linux/vhost.h | 6 ++++
4 files changed, 117 insertions(+), 5 deletions(-)
--
1.8.3.1
This path introduces a helper which can give a hint for whether or not
there's a work queued in the work list. This could be used for busy
polling code to exit the busy loop.
Signed-off-by: Jason Wang <[email protected]>
---
drivers/vhost/vhost.c | 7 +++++++
drivers/vhost/vhost.h | 1 +
2 files changed, 8 insertions(+)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ad2146a..90ac092 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -245,6 +245,13 @@ void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
}
EXPORT_SYMBOL_GPL(vhost_work_queue);
+/* A lockless hint for busy polling code to exit the loop */
+bool vhost_has_work(struct vhost_dev *dev)
+{
+ return !list_empty(&dev->work_list);
+}
+EXPORT_SYMBOL_GPL(vhost_has_work);
+
void vhost_poll_queue(struct vhost_poll *poll)
{
vhost_work_queue(poll->dev, &poll->work);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index d3f7674..43284ad 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -37,6 +37,7 @@ struct vhost_poll {
void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn);
void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work);
+bool vhost_has_work(struct vhost_dev *dev);
void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
unsigned long mask, struct vhost_dev *dev);
--
1.8.3.1
This patch tries to poll for new added tx buffer or socket receive
queue for a while at the end of tx/rx processing. The maximum time
spent on polling were specified through a new kind of vring ioctl.
Signed-off-by: Jason Wang <[email protected]>
---
drivers/vhost/net.c | 78 +++++++++++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.c | 14 +++++++++
drivers/vhost/vhost.h | 1 +
include/uapi/linux/vhost.h | 6 ++++
4 files changed, 94 insertions(+), 5 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9eda69e..eefdbc7 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -287,6 +287,43 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
rcu_read_unlock_bh();
}
+static inline unsigned long busy_clock(void)
+{
+ return local_clock() >> 10;
+}
+
+static bool vhost_can_busy_poll(struct vhost_dev *dev,
+ unsigned long endtime)
+{
+ return likely(!need_resched()) &&
+ likely(!time_after(busy_clock(), endtime)) &&
+ likely(!signal_pending(current)) &&
+ !vhost_has_work(dev);
+}
+
+static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
+ struct vhost_virtqueue *vq,
+ struct iovec iov[], unsigned int iov_size,
+ unsigned int *out_num, unsigned int *in_num)
+{
+ unsigned long uninitialized_var(endtime);
+ int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+ out_num, in_num, NULL, NULL);
+
+ if (r == vq->num && vq->busyloop_timeout) {
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+ while (vhost_can_busy_poll(vq->dev, endtime) &&
+ vhost_vq_avail_empty(vq->dev, vq))
+ cpu_relax_lowlatency();
+ preempt_enable();
+ r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+ out_num, in_num, NULL, NULL);
+ }
+
+ return r;
+}
+
/* Expects to be always run from workqueue - which acts as
* read-size critical section for our kind of RCU. */
static void handle_tx(struct vhost_net *net)
@@ -331,10 +368,9 @@ static void handle_tx(struct vhost_net *net)
% UIO_MAXIOV == nvq->done_idx))
break;
- head = vhost_get_vq_desc(vq, vq->iov,
- ARRAY_SIZE(vq->iov),
- &out, &in,
- NULL, NULL);
+ head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in);
/* On error, stop handling until the next kick. */
if (unlikely(head < 0))
break;
@@ -435,6 +471,38 @@ static int peek_head_len(struct sock *sk)
return len;
}
+static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
+{
+ struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
+ struct vhost_virtqueue *vq = &nvq->vq;
+ unsigned long uninitialized_var(endtime);
+ int len = peek_head_len(sk);
+
+ if (!len && vq->busyloop_timeout) {
+ /* Both tx vq and rx socket were polled here */
+ mutex_lock(&vq->mutex);
+ vhost_disable_notify(&net->dev, vq);
+
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+
+ while (vhost_can_busy_poll(&net->dev, endtime) &&
+ skb_queue_empty(&sk->sk_receive_queue) &&
+ vhost_vq_avail_empty(&net->dev, vq))
+ cpu_relax_lowlatency();
+
+ preempt_enable();
+
+ if (vhost_enable_notify(&net->dev, vq))
+ vhost_poll_queue(&vq->poll);
+ mutex_unlock(&vq->mutex);
+
+ len = peek_head_len(sk);
+ }
+
+ return len;
+}
+
/* This is a multi-buffer version of vhost_get_desc, that works if
* vq has read descriptors only.
* @vq - the relevant virtqueue
@@ -553,7 +621,7 @@ static void handle_rx(struct vhost_net *net)
vq->log : NULL;
mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
- while ((sock_len = peek_head_len(sock->sk))) {
+ while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk))) {
sock_len += sock_hlen;
vhost_len = sock_len + vhost_hlen;
headcount = get_rx_bufs(vq, vq->heads, vhost_len,
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 89301fd..b4b7eda 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -285,6 +285,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->memory = NULL;
vq->is_le = virtio_legacy_is_little_endian();
vhost_vq_reset_user_be(vq);
+ vq->busyloop_timeout = 0;
}
static int vhost_worker(void *data)
@@ -919,6 +920,19 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
case VHOST_GET_VRING_ENDIAN:
r = vhost_get_vring_endian(vq, idx, argp);
break;
+ case VHOST_SET_VRING_BUSYLOOP_TIMEOUT:
+ if (copy_from_user(&s, argp, sizeof(s))) {
+ r = -EFAULT;
+ break;
+ }
+ vq->busyloop_timeout = s.num;
+ break;
+ case VHOST_GET_VRING_BUSYLOOP_TIMEOUT:
+ s.index = idx;
+ s.num = vq->busyloop_timeout;
+ if (copy_to_user(argp, &s, sizeof(s)))
+ r = -EFAULT;
+ break;
default:
r = -ENOIOCTLCMD;
}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a7a43f0..9a02158 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -115,6 +115,7 @@ struct vhost_virtqueue {
/* Ring endianness requested by userspace for cross-endian support. */
bool user_be;
#endif
+ u32 busyloop_timeout;
};
struct vhost_dev {
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index ab373191..61a8777 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -126,6 +126,12 @@ struct vhost_memory {
#define VHOST_SET_VRING_CALL _IOW(VHOST_VIRTIO, 0x21, struct vhost_vring_file)
/* Set eventfd to signal an error */
#define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file)
+/* Set busy loop timeout (in us) */
+#define VHOST_SET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x23, \
+ struct vhost_vring_state)
+/* Get busy loop timeout (in us) */
+#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24, \
+ struct vhost_vring_state)
/* VHOST_NET specific defines */
--
1.8.3.1
This patch introduces a helper which will return true if we're sure
that the available ring is empty for a specific vq. When we're not
sure, e.g vq access failure, return false instead. This could be used
for busy polling code to exit the busy loop.
Signed-off-by: Jason Wang <[email protected]>
---
drivers/vhost/vhost.c | 14 ++++++++++++++
drivers/vhost/vhost.h | 1 +
2 files changed, 15 insertions(+)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 90ac092..89301fd 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1633,6 +1633,20 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev,
}
EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
+/* return true if we're sure that avaiable ring is empty */
+bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+ __virtio16 avail_idx;
+ int r;
+
+ r = __get_user(avail_idx, &vq->avail->idx);
+ if (r)
+ return false;
+
+ return vhost16_to_cpu(vq, avail_idx) == vq->avail_idx;
+}
+EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);
+
/* OK, now we need to know about added descriptors. */
bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 43284ad..a7a43f0 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -159,6 +159,7 @@ void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
struct vring_used_elem *heads, unsigned count);
void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
+bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
--
1.8.3.1
On Fri, 4 Mar 2016 06:24:50 -0500
Jason Wang <[email protected]> wrote:
> This series tries to add basic busy polling for vhost net. The idea is
> simple: at the end of tx/rx processing, busy polling for new tx added
> descriptor and rx receive socket for a while. The maximum number of
> time (in us) could be spent on busy polling was specified ioctl.
>
> Test A were done through:
>
> - 50 us as busy loop timeout
> - Netperf 2.6
> - Two machines with back to back connected mlx4
Hi Jason,
Could this also improve performance if both VMs are
on the same host system ?
> - Guest with 1 vcpus and 1 queue
>
> Results:
> - Obvious improvements (%5 - 20%) for latency (TCP_RR).
> - Get a better or minor regression on most of the TX tests, but see
> some regression on 4096 size.
> - Except for 8 sessions of 4096 size RX, have a better or same
> performance.
> - CPU utilization were incrased as expected.
>
> TCP_RR:
> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
> 1/ 1/ +8%/ -32%/ +8%/ +8%/ +7%
> 1/ 50/ +7%/ -19%/ +7%/ +7%/ +1%
> 1/ 100/ +5%/ -21%/ +5%/ +5%/ 0%
> 1/ 200/ +5%/ -21%/ +7%/ +7%/ +1%
> 64/ 1/ +11%/ -29%/ +11%/ +11%/ +10%
> 64/ 50/ +7%/ -19%/ +8%/ +8%/ +2%
> 64/ 100/ +8%/ -18%/ +9%/ +9%/ +2%
> 64/ 200/ +6%/ -19%/ +6%/ +6%/ 0%
> 256/ 1/ +7%/ -33%/ +7%/ +7%/ +6%
> 256/ 50/ +7%/ -18%/ +7%/ +7%/ 0%
> 256/ 100/ +9%/ -18%/ +8%/ +8%/ +2%
> 256/ 200/ +9%/ -18%/ +10%/ +10%/ +3%
> 1024/ 1/ +20%/ -28%/ +20%/ +20%/ +19%
> 1024/ 50/ +8%/ -18%/ +9%/ +9%/ +2%
> 1024/ 100/ +6%/ -19%/ +5%/ +5%/ 0%
> 1024/ 200/ +8%/ -18%/ +9%/ +9%/ +2%
> Guest TX:
> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
> 64/ 1/ -5%/ -28%/ +11%/ +12%/ +10%
> 64/ 4/ -2%/ -26%/ +13%/ +13%/ +13%
> 64/ 8/ -6%/ -29%/ +9%/ +10%/ +10%
> 512/ 1/ +15%/ -7%/ +13%/ +11%/ +3%
> 512/ 4/ +17%/ -6%/ +18%/ +13%/ +11%
> 512/ 8/ +14%/ -7%/ +13%/ +7%/ +7%
> 1024/ 1/ +27%/ -2%/ +26%/ +29%/ +12%
> 1024/ 4/ +8%/ -9%/ +6%/ +1%/ +6%
> 1024/ 8/ +41%/ +12%/ +34%/ +20%/ -3%
> 4096/ 1/ -22%/ -21%/ -36%/ +81%/+1360%
> 4096/ 4/ -57%/ -58%/ +286%/ +15%/+2074%
> 4096/ 8/ +67%/ +70%/ -45%/ -8%/ +63%
> 16384/ 1/ -2%/ -5%/ +5%/ -3%/ +80%
> 16384/ 4/ 0%/ 0%/ 0%/ +4%/ +138%
> 16384/ 8/ 0%/ 0%/ 0%/ +1%/ +41%
> 65535/ 1/ -3%/ -6%/ +2%/ +11%/ +113%
> 65535/ 4/ -2%/ -1%/ -2%/ -3%/ +484%
> 65535/ 8/ 0%/ +1%/ 0%/ +2%/ +40%
> Guest RX:
> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
> 64/ 1/ +31%/ -3%/ +8%/ +8%/ +8%
> 64/ 4/ +11%/ -17%/ +13%/ +14%/ +15%
> 64/ 8/ +4%/ -23%/ +11%/ +11%/ +12%
> 512/ 1/ +24%/ 0%/ +18%/ +14%/ -8%
> 512/ 4/ +4%/ -15%/ +6%/ +5%/ +6%
> 512/ 8/ +26%/ 0%/ +21%/ +10%/ +3%
> 1024/ 1/ +88%/ +47%/ +69%/ +44%/ -30%
> 1024/ 4/ +18%/ -5%/ +19%/ +16%/ +2%
> 1024/ 8/ +15%/ -4%/ +13%/ +8%/ +1%
> 4096/ 1/ -3%/ -5%/ +2%/ -2%/ +41%
> 4096/ 4/ +2%/ +3%/ -20%/ -14%/ -24%
> 4096/ 8/ -43%/ -45%/ +69%/ -24%/ +94%
> 16384/ 1/ -3%/ -11%/ +23%/ +7%/ +42%
> 16384/ 4/ -3%/ -3%/ -4%/ +5%/ +115%
> 16384/ 8/ -1%/ 0%/ -1%/ -3%/ +32%
> 65535/ 1/ +1%/ 0%/ +2%/ 0%/ +66%
> 65535/ 4/ -1%/ -1%/ 0%/ +4%/ +492%
> 65535/ 8/ 0%/ -1%/ -1%/ +4%/ +38%
>
> Changes from V3:
> - drop single_task_running()
> - use cpu_relax_lowlatency() instead of cpu_relax()
>
> Changes from V2:
> - rename vhost_vq_more_avail() to vhost_vq_avail_empty(). And return
> false we __get_user() fails.
> - do not bother premmptions/timers for good path.
> - use vhost_vring_state as ioctl parameter instead of reinveting a new
> one.
> - add the unit of timeout (us) to the comment of new added ioctls
>
> Changes from V1:
> - remove the buggy vq_error() in vhost_vq_more_avail().
> - leave vhost_enable_notify() untouched.
>
> Changes from RFC V3:
> - small tweak on the code to avoid multiple duplicate conditions in
> critical path when busy loop is not enabled.
> - add the test result of multiple VMs
>
> Changes from RFC V2:
> - poll also at the end of rx handling
> - factor out the polling logic and optimize the code a little bit
> - add two ioctls to get and set the busy poll timeout
> - test on ixgbe (which can give more stable and reproducable numbers)
> instead of mlx4.
>
> Changes from RFC V1:
> - add a comment for vhost_has_work() to explain why it could be
> lockless
> - add param description for busyloop_timeout
> - split out the busy polling logic into a new helper
> - check and exit the loop when there's a pending signal
> - disable preemption during busy looping to make sure lock_clock() was
> correctly used.
>
> Jason Wang (3):
> vhost: introduce vhost_has_work()
> vhost: introduce vhost_vq_avail_empty()
> vhost_net: basic polling support
>
> drivers/vhost/net.c | 78 +++++++++++++++++++++++++++++++++++++++++++---
> drivers/vhost/vhost.c | 35 +++++++++++++++++++++
> drivers/vhost/vhost.h | 3 ++
> include/uapi/linux/vhost.h | 6 ++++
> 4 files changed, 117 insertions(+), 5 deletions(-)
>
Hi Greg,
> Greg Kurz <[email protected]> wrote on 03/09/2016 09:26:45 PM:
> > On Fri, 4 Mar 2016 06:24:50 -0500
> > Jason Wang <[email protected]> wrote:
>
> > This series tries to add basic busy polling for vhost net. The idea is
> > simple: at the end of tx/rx processing, busy polling for new tx added
> > descriptor and rx receive socket for a while. The maximum number of
> > time (in us) could be spent on busy polling was specified ioctl.
> >
> > Test A were done through:
> >
> > - 50 us as busy loop timeout
> > - Netperf 2.6
> > - Two machines with back to back connected mlx4
>
> Hi Jason,
>
> Could this also improve performance if both VMs are
> on the same host system ?
I've experimented a little with Jason's patches and guest-to-guest netperf
when both guests were on the same host, and I saw improvements for that
case.
> > - Guest with 1 vcpus and 1 queue
> >
> > Results:
> > - Obvious improvements (%5 - 20%) for latency (TCP_RR).
> > - Get a better or minor regression on most of the TX tests, but see
> > some regression on 4096 size.
> > - Except for 8 sessions of 4096 size RX, have a better or same
> > performance.
> > - CPU utilization were incrased as expected.
> >
> > TCP_RR:
> > size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
> > 1/ 1/ +8%/ -32%/ +8%/ +8%/ +7%
> > 1/ 50/ +7%/ -19%/ +7%/ +7%/ +1%
> > 1/ 100/ +5%/ -21%/ +5%/ +5%/ 0%
> > 1/ 200/ +5%/ -21%/ +7%/ +7%/ +1%
> > 64/ 1/ +11%/ -29%/ +11%/ +11%/ +10%
> > 64/ 50/ +7%/ -19%/ +8%/ +8%/ +2%
> > 64/ 100/ +8%/ -18%/ +9%/ +9%/ +2%
> > 64/ 200/ +6%/ -19%/ +6%/ +6%/ 0%
> > 256/ 1/ +7%/ -33%/ +7%/ +7%/ +6%
> > 256/ 50/ +7%/ -18%/ +7%/ +7%/ 0%
> > 256/ 100/ +9%/ -18%/ +8%/ +8%/ +2%
> > 256/ 200/ +9%/ -18%/ +10%/ +10%/ +3%
> > 1024/ 1/ +20%/ -28%/ +20%/ +20%/ +19%
> > 1024/ 50/ +8%/ -18%/ +9%/ +9%/ +2%
> > 1024/ 100/ +6%/ -19%/ +5%/ +5%/ 0%
> > 1024/ 200/ +8%/ -18%/ +9%/ +9%/ +2%
> > Guest TX:
> > size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
> > 64/ 1/ -5%/ -28%/ +11%/ +12%/ +10%
> > 64/ 4/ -2%/ -26%/ +13%/ +13%/ +13%
> > 64/ 8/ -6%/ -29%/ +9%/ +10%/ +10%
> > 512/ 1/ +15%/ -7%/ +13%/ +11%/ +3%
> > 512/ 4/ +17%/ -6%/ +18%/ +13%/ +11%
> > 512/ 8/ +14%/ -7%/ +13%/ +7%/ +7%
> > 1024/ 1/ +27%/ -2%/ +26%/ +29%/ +12%
> > 1024/ 4/ +8%/ -9%/ +6%/ +1%/ +6%
> > 1024/ 8/ +41%/ +12%/ +34%/ +20%/ -3%
> > 4096/ 1/ -22%/ -21%/ -36%/ +81%/+1360%
> > 4096/ 4/ -57%/ -58%/ +286%/ +15%/+2074%
> > 4096/ 8/ +67%/ +70%/ -45%/ -8%/ +63%
> > 16384/ 1/ -2%/ -5%/ +5%/ -3%/ +80%
> > 16384/ 4/ 0%/ 0%/ 0%/ +4%/ +138%
> > 16384/ 8/ 0%/ 0%/ 0%/ +1%/ +41%
> > 65535/ 1/ -3%/ -6%/ +2%/ +11%/ +113%
> > 65535/ 4/ -2%/ -1%/ -2%/ -3%/ +484%
> > 65535/ 8/ 0%/ +1%/ 0%/ +2%/ +40%
> > Guest RX:
> > size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
> > 64/ 1/ +31%/ -3%/ +8%/ +8%/ +8%
> > 64/ 4/ +11%/ -17%/ +13%/ +14%/ +15%
> > 64/ 8/ +4%/ -23%/ +11%/ +11%/ +12%
> > 512/ 1/ +24%/ 0%/ +18%/ +14%/ -8%
> > 512/ 4/ +4%/ -15%/ +6%/ +5%/ +6%
> > 512/ 8/ +26%/ 0%/ +21%/ +10%/ +3%
> > 1024/ 1/ +88%/ +47%/ +69%/ +44%/ -30%
> > 1024/ 4/ +18%/ -5%/ +19%/ +16%/ +2%
> > 1024/ 8/ +15%/ -4%/ +13%/ +8%/ +1%
> > 4096/ 1/ -3%/ -5%/ +2%/ -2%/ +41%
> > 4096/ 4/ +2%/ +3%/ -20%/ -14%/ -24%
> > 4096/ 8/ -43%/ -45%/ +69%/ -24%/ +94%
> > 16384/ 1/ -3%/ -11%/ +23%/ +7%/ +42%
> > 16384/ 4/ -3%/ -3%/ -4%/ +5%/ +115%
> > 16384/ 8/ -1%/ 0%/ -1%/ -3%/ +32%
> > 65535/ 1/ +1%/ 0%/ +2%/ 0%/ +66%
> > 65535/ 4/ -1%/ -1%/ 0%/ +4%/ +492%
> > 65535/ 8/ 0%/ -1%/ -1%/ +4%/ +38%
> >
> > Changes from V3:
> > - drop single_task_running()
> > - use cpu_relax_lowlatency() instead of cpu_relax()
> >
> > Changes from V2:
> > - rename vhost_vq_more_avail() to vhost_vq_avail_empty(). And return
> > false we __get_user() fails.
> > - do not bother premmptions/timers for good path.
> > - use vhost_vring_state as ioctl parameter instead of reinveting a new
> > one.
> > - add the unit of timeout (us) to the comment of new added ioctls
> >
> > Changes from V1:
> > - remove the buggy vq_error() in vhost_vq_more_avail().
> > - leave vhost_enable_notify() untouched.
> >
> > Changes from RFC V3:
> > - small tweak on the code to avoid multiple duplicate conditions in
> > critical path when busy loop is not enabled.
> > - add the test result of multiple VMs
> >
> > Changes from RFC V2:
> > - poll also at the end of rx handling
> > - factor out the polling logic and optimize the code a little bit
> > - add two ioctls to get and set the busy poll timeout
> > - test on ixgbe (which can give more stable and reproducable numbers)
> > instead of mlx4.
> >
> > Changes from RFC V1:
> > - add a comment for vhost_has_work() to explain why it could be
> > lockless
> > - add param description for busyloop_timeout
> > - split out the busy polling logic into a new helper
> > - check and exit the loop when there's a pending signal
> > - disable preemption during busy looping to make sure lock_clock() was
> > correctly used.
> >
> > Jason Wang (3):
> > vhost: introduce vhost_has_work()
> > vhost: introduce vhost_vq_avail_empty()
> > vhost_net: basic polling support
> >
> > drivers/vhost/net.c | 78
+++++++++++++++++++++++++++++++++++++++++++---
> > drivers/vhost/vhost.c | 35 +++++++++++++++++++++
> > drivers/vhost/vhost.h | 3 ++
> > include/uapi/linux/vhost.h | 6 ++++
> > 4 files changed, 117 insertions(+), 5 deletions(-)
> >
>
On 03/10/2016 02:48 PM, Michael Rapoport wrote:
> Hi Greg,
>
>> > Greg Kurz <[email protected]> wrote on 03/09/2016 09:26:45 PM:
>>> > > On Fri, 4 Mar 2016 06:24:50 -0500
>>> > > Jason Wang <[email protected]> wrote:
>> >
>>> > > This series tries to add basic busy polling for vhost net. The idea is
>>> > > simple: at the end of tx/rx processing, busy polling for new tx added
>>> > > descriptor and rx receive socket for a while. The maximum number of
>>> > > time (in us) could be spent on busy polling was specified ioctl.
>>> > >
>>> > > Test A were done through:
>>> > >
>>> > > - 50 us as busy loop timeout
>>> > > - Netperf 2.6
>>> > > - Two machines with back to back connected mlx4
>> >
>> > Hi Jason,
>> >
>> > Could this also improve performance if both VMs are
>> > on the same host system ?
> I've experimented a little with Jason's patches and guest-to-guest netperf
> when both guests were on the same host, and I saw improvements for that
> case.
>
Good to know this, I haven't tested this before but from the codes, it
should work for VM2VM case too.
Thanks a lot for the testing.