vfio_pin_pages() accepts an array of unrelated iova pfns and processes
each to return the physical pfn. When dealing with large arrays of
contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
it is processed page by page.In this case, we can divide the iova pfn
array into multiple continuous ranges and optimize them. For example,
when the iova pfn array is {1,5,6,7,9}, it will be divided into three
groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
number of calls to pin_user_pages_remote is reduced from 3 times to once.
For single page or large array of discontinuous iovas, we still use
vfio_pin_page_external to deal with it to reduce the performance loss
caused by refactoring.
Signed-off-by: Xiaoyang Xu <[email protected]>
---
v1 -> v2:
* make vfio_iommu_type1_pin_contiguous_pages use vfio_pin_page_external
to pin single page when npage=1
* make vfio_pin_contiguous_pages_external use set npage to mark
consecutive pages as dirty. simplify the processing logic of unwind
* remove unnecessary checks in vfio_get_contiguous_pages_length, put
the least costly judgment logic at the top, and replace
vfio_iova_get_vfio_pfn with vfio_find_vpfn
drivers/vfio/vfio_iommu_type1.c | 231 ++++++++++++++++++++++++++++----
1 file changed, 204 insertions(+), 27 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 67e827638995..080727b531c6 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -628,6 +628,196 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
return unlocked;
}
+static int contiguous_vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
+ int prot, long npage, unsigned long *phys_pfn)
+{
+ struct page **pages = NULL;
+ unsigned int flags = 0;
+ int i, ret;
+
+ pages = kvmalloc_array(npage, sizeof(struct page *), GFP_KERNEL);
+ if (!pages)
+ return -ENOMEM;
+
+ if (prot & IOMMU_WRITE)
+ flags |= FOLL_WRITE;
+
+ mmap_read_lock(mm);
+ ret = pin_user_pages_remote(mm, vaddr, npage, flags | FOLL_LONGTERM,
+ pages, NULL, NULL);
+ mmap_read_unlock(mm);
+
+ for (i = 0; i < ret; i++)
+ *(phys_pfn + i) = page_to_pfn(pages[i]);
+
+ kvfree(pages);
+
+ return ret;
+}
+
+static int vfio_pin_contiguous_pages_external(struct vfio_iommu *iommu,
+ struct vfio_dma *dma,
+ unsigned long *user_pfn,
+ int npage, unsigned long *phys_pfn,
+ bool do_accounting)
+{
+ int ret, i, j, lock_acct = 0;
+ unsigned long remote_vaddr;
+ dma_addr_t iova;
+ struct mm_struct *mm;
+ struct vfio_pfn *vpfn;
+
+ mm = get_task_mm(dma->task);
+ if (!mm)
+ return -ENODEV;
+
+ iova = user_pfn[0] << PAGE_SHIFT;
+ remote_vaddr = dma->vaddr + iova - dma->iova;
+ ret = contiguous_vaddr_get_pfn(mm, remote_vaddr, dma->prot,
+ npage, phys_pfn);
+ mmput(mm);
+ if (ret <= 0)
+ return ret;
+
+ npage = ret;
+ for (i = 0; i < npage; i++) {
+ iova = user_pfn[i] << PAGE_SHIFT;
+ ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
+ if (ret)
+ goto unwind;
+
+ if (!is_invalid_reserved_pfn(phys_pfn[i]))
+ lock_acct++;
+ }
+
+ if (do_accounting) {
+ ret = vfio_lock_acct(dma, lock_acct, true);
+ if (ret) {
+ if (ret == -ENOMEM)
+ pr_warn("%s: Task %s (%d) RLIMIT_MEMLOCK (%ld) exceeded\n",
+ __func__, dma->task->comm, task_pid_nr(dma->task),
+ task_rlimit(dma->task, RLIMIT_MEMLOCK));
+ goto unwind;
+ }
+ }
+
+ if (iommu->dirty_page_tracking) {
+ unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
+
+ /*
+ * Bitmap populated with the smallest supported page
+ * size
+ */
+ bitmap_set(dma->bitmap,
+ ((user_pfn[0] << PAGE_SHIFT) - dma->iova) >> pgshift, npage);
+ }
+
+ return i;
+unwind:
+ for (j = 0; j < npage; j++) {
+ if (j < i) {
+ iova = user_pfn[j] << PAGE_SHIFT;
+ vpfn = vfio_find_vpfn(dma, iova);
+ vfio_iova_put_vfio_pfn(dma, vpfn);
+ } else {
+ put_pfn(phys_pfn[j], dma->prot);
+ }
+
+ phys_pfn[j] = 0;
+ }
+
+ return ret;
+}
+
+static int vfio_iommu_type1_pin_contiguous_pages(struct vfio_iommu *iommu,
+ struct vfio_dma *dma,
+ unsigned long *user_pfn,
+ int npage, unsigned long *phys_pfn,
+ bool do_accounting)
+{
+ int ret = 0, i, j;
+ unsigned long remote_vaddr;
+ dma_addr_t iova;
+
+ if (npage == 1)
+ goto pin_single_page;
+
+ ret = vfio_pin_contiguous_pages_external(iommu, dma, user_pfn, npage,
+ phys_pfn, do_accounting);
+ if (ret == npage)
+ return ret;
+
+ if (ret < 0)
+ ret = 0;
+
+pin_single_page:
+ for (i = ret; i < npage; i++) {
+ iova = user_pfn[i] << PAGE_SHIFT;
+ remote_vaddr = dma->vaddr + iova - dma->iova;
+
+ ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn[i],
+ do_accounting);
+ if (ret)
+ goto pin_unwind;
+
+ ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
+ if (ret) {
+ if (put_pfn(phys_pfn[i], dma->prot) && do_accounting)
+ vfio_lock_acct(dma, -1, true);
+ goto pin_unwind;
+ }
+
+ if (iommu->dirty_page_tracking) {
+ unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
+
+ /*
+ * Bitmap populated with the smallest supported page
+ * size
+ */
+ bitmap_set(dma->bitmap,
+ (iova - dma->iova) >> pgshift, 1);
+ }
+ }
+
+ return i;
+
+pin_unwind:
+ phys_pfn[i] = 0;
+ for (j = 0; j < i; j++) {
+ iova = user_pfn[j] << PAGE_SHIFT;
+ vfio_unpin_page_external(dma, iova, do_accounting);
+ phys_pfn[j] = 0;
+ }
+
+ return ret;
+}
+
+static int vfio_get_contiguous_pages_length(struct vfio_dma *dma,
+ unsigned long *user_pfn, int npage)
+{
+ int i;
+ dma_addr_t iova = user_pfn[0] << PAGE_SHIFT;
+ struct vfio_pfn *vpfn;
+
+ if (npage <= 1)
+ return npage;
+
+ for (i = 1; i < npage; i++) {
+ if (user_pfn[i] != user_pfn[0] + i)
+ break;
+
+ iova = user_pfn[i] << PAGE_SHIFT;
+ if (iova >= dma->iova + dma->size ||
+ iova + PAGE_SIZE <= dma->iova)
+ break;
+
+ vpfn = vfio_find_vpfn(dma, iova);
+ if (vpfn)
+ break;
+ }
+ return i;
+}
+
static int vfio_iommu_type1_pin_pages(void *iommu_data,
struct iommu_group *iommu_group,
unsigned long *user_pfn,
@@ -637,9 +827,9 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
struct vfio_iommu *iommu = iommu_data;
struct vfio_group *group;
int i, j, ret;
- unsigned long remote_vaddr;
struct vfio_dma *dma;
bool do_accounting;
+ int contiguous_npage;
if (!iommu || !user_pfn || !phys_pfn)
return -EINVAL;
@@ -663,7 +853,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
*/
do_accounting = !IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu);
- for (i = 0; i < npage; i++) {
+ for (i = 0; i < npage; i += contiguous_npage) {
dma_addr_t iova;
struct vfio_pfn *vpfn;
@@ -682,31 +872,18 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
vpfn = vfio_iova_get_vfio_pfn(dma, iova);
if (vpfn) {
phys_pfn[i] = vpfn->pfn;
- continue;
- }
-
- remote_vaddr = dma->vaddr + (iova - dma->iova);
- ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn[i],
- do_accounting);
- if (ret)
- goto pin_unwind;
-
- ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
- if (ret) {
- if (put_pfn(phys_pfn[i], dma->prot) && do_accounting)
- vfio_lock_acct(dma, -1, true);
- goto pin_unwind;
- }
-
- if (iommu->dirty_page_tracking) {
- unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
-
- /*
- * Bitmap populated with the smallest supported page
- * size
- */
- bitmap_set(dma->bitmap,
- (iova - dma->iova) >> pgshift, 1);
+ contiguous_npage = 1;
+ } else {
+ ret = vfio_get_contiguous_pages_length(dma,
+ &user_pfn[i], npage - i);
+ if (ret < 0)
+ goto pin_unwind;
+
+ ret = vfio_iommu_type1_pin_contiguous_pages(iommu,
+ dma, &user_pfn[i], ret, &phys_pfn[i], do_accounting);
+ if (ret < 0)
+ goto pin_unwind;
+ contiguous_npage = ret;
}
}
ret = i;
--
2.19.1
On 2020/11/21 15:58, xuxiaoyang (C) wrote:
> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
> each to return the physical pfn. When dealing with large arrays of
> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
> it is processed page by page.In this case, we can divide the iova pfn
> array into multiple continuous ranges and optimize them. For example,
> when the iova pfn array is {1,5,6,7,9}, it will be divided into three
> groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
> number of calls to pin_user_pages_remote is reduced from 3 times to once.
> For single page or large array of discontinuous iovas, we still use
> vfio_pin_page_external to deal with it to reduce the performance loss
> caused by refactoring.
>
> Signed-off-by: Xiaoyang Xu <[email protected]>
> ---
> v1 -> v2:
> * make vfio_iommu_type1_pin_contiguous_pages use vfio_pin_page_external
> to pin single page when npage=1
> * make vfio_pin_contiguous_pages_external use set npage to mark
> consecutive pages as dirty. simplify the processing logic of unwind
> * remove unnecessary checks in vfio_get_contiguous_pages_length, put
> the least costly judgment logic at the top, and replace
> vfio_iova_get_vfio_pfn with vfio_find_vpfn
>
> drivers/vfio/vfio_iommu_type1.c | 231 ++++++++++++++++++++++++++++----
> 1 file changed, 204 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 67e827638995..080727b531c6 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -628,6 +628,196 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, dma_addr_t iova,
> return unlocked;
> }
>
> +static int contiguous_vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> + int prot, long npage, unsigned long *phys_pfn)
> +{
> + struct page **pages = NULL;
> + unsigned int flags = 0;
> + int i, ret;
> +
> + pages = kvmalloc_array(npage, sizeof(struct page *), GFP_KERNEL);
> + if (!pages)
> + return -ENOMEM;
> +
> + if (prot & IOMMU_WRITE)
> + flags |= FOLL_WRITE;
> +
> + mmap_read_lock(mm);
> + ret = pin_user_pages_remote(mm, vaddr, npage, flags | FOLL_LONGTERM,
> + pages, NULL, NULL);
> + mmap_read_unlock(mm);
> +
> + for (i = 0; i < ret; i++)
> + *(phys_pfn + i) = page_to_pfn(pages[i]);
> +
> + kvfree(pages);
> +
> + return ret;
> +}
> +
> +static int vfio_pin_contiguous_pages_external(struct vfio_iommu *iommu,
> + struct vfio_dma *dma,
> + unsigned long *user_pfn,
> + int npage, unsigned long *phys_pfn,
> + bool do_accounting)
> +{
> + int ret, i, j, lock_acct = 0;
> + unsigned long remote_vaddr;
> + dma_addr_t iova;
> + struct mm_struct *mm;
> + struct vfio_pfn *vpfn;
> +
> + mm = get_task_mm(dma->task);
> + if (!mm)
> + return -ENODEV;
> +
> + iova = user_pfn[0] << PAGE_SHIFT;
> + remote_vaddr = dma->vaddr + iova - dma->iova;
> + ret = contiguous_vaddr_get_pfn(mm, remote_vaddr, dma->prot,
> + npage, phys_pfn);
> + mmput(mm);
> + if (ret <= 0)
> + return ret;
> +
> + npage = ret;
> + for (i = 0; i < npage; i++) {
> + iova = user_pfn[i] << PAGE_SHIFT;
> + ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> + if (ret)
> + goto unwind;
> +
> + if (!is_invalid_reserved_pfn(phys_pfn[i]))
> + lock_acct++;
> + }
> +
> + if (do_accounting) {
> + ret = vfio_lock_acct(dma, lock_acct, true);
> + if (ret) {
> + if (ret == -ENOMEM)
> + pr_warn("%s: Task %s (%d) RLIMIT_MEMLOCK (%ld) exceeded\n",
> + __func__, dma->task->comm, task_pid_nr(dma->task),
> + task_rlimit(dma->task, RLIMIT_MEMLOCK));
> + goto unwind;
> + }
> + }
> +
> + if (iommu->dirty_page_tracking) {
> + unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
> +
> + /*
> + * Bitmap populated with the smallest supported page
> + * size
> + */
> + bitmap_set(dma->bitmap,
> + ((user_pfn[0] << PAGE_SHIFT) - dma->iova) >> pgshift, npage);
> + }
> +
> + return i;
> +unwind:
> + for (j = 0; j < npage; j++) {
> + if (j < i) {
> + iova = user_pfn[j] << PAGE_SHIFT;
> + vpfn = vfio_find_vpfn(dma, iova);
> + vfio_iova_put_vfio_pfn(dma, vpfn);
> + } else {
> + put_pfn(phys_pfn[j], dma->prot);
> + }
> +
> + phys_pfn[j] = 0;
> + }
> +
> + return ret;
> +}
> +
> +static int vfio_iommu_type1_pin_contiguous_pages(struct vfio_iommu *iommu,
> + struct vfio_dma *dma,
> + unsigned long *user_pfn,
> + int npage, unsigned long *phys_pfn,
> + bool do_accounting)
> +{
> + int ret = 0, i, j;
> + unsigned long remote_vaddr;
> + dma_addr_t iova;
> +
> + if (npage == 1)
> + goto pin_single_page;
> +
> + ret = vfio_pin_contiguous_pages_external(iommu, dma, user_pfn, npage,
> + phys_pfn, do_accounting);
> + if (ret == npage)
> + return ret;
> +
> + if (ret < 0)
> + ret = 0;
> +
> +pin_single_page:
> + for (i = ret; i < npage; i++) {
> + iova = user_pfn[i] << PAGE_SHIFT;
> + remote_vaddr = dma->vaddr + iova - dma->iova;
> +
> + ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn[i],
> + do_accounting);
> + if (ret)
> + goto pin_unwind;
> +
> + ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> + if (ret) {
> + if (put_pfn(phys_pfn[i], dma->prot) && do_accounting)
> + vfio_lock_acct(dma, -1, true);
> + goto pin_unwind;
> + }
> +
> + if (iommu->dirty_page_tracking) {
> + unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
> +
> + /*
> + * Bitmap populated with the smallest supported page
> + * size
> + */
> + bitmap_set(dma->bitmap,
> + (iova - dma->iova) >> pgshift, 1);
> + }
> + }
> +
> + return i;
> +
> +pin_unwind:
> + phys_pfn[i] = 0;
> + for (j = 0; j < i; j++) {
> + iova = user_pfn[j] << PAGE_SHIFT;
> + vfio_unpin_page_external(dma, iova, do_accounting);
> + phys_pfn[j] = 0;
> + }
> +
> + return ret;
> +}
> +
> +static int vfio_get_contiguous_pages_length(struct vfio_dma *dma,
> + unsigned long *user_pfn, int npage)
> +{
> + int i;
> + dma_addr_t iova = user_pfn[0] << PAGE_SHIFT;
> + struct vfio_pfn *vpfn;
> +
> + if (npage <= 1)
> + return npage;
> +
> + for (i = 1; i < npage; i++) {
> + if (user_pfn[i] != user_pfn[0] + i)
> + break;
> +
> + iova = user_pfn[i] << PAGE_SHIFT;
> + if (iova >= dma->iova + dma->size ||
> + iova + PAGE_SIZE <= dma->iova)
> + break;
> +
> + vpfn = vfio_find_vpfn(dma, iova);
> + if (vpfn)
> + break;
> + }
> + return i;
> +}
> +
> static int vfio_iommu_type1_pin_pages(void *iommu_data,
> struct iommu_group *iommu_group,
> unsigned long *user_pfn,
> @@ -637,9 +827,9 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> struct vfio_iommu *iommu = iommu_data;
> struct vfio_group *group;
> int i, j, ret;
> - unsigned long remote_vaddr;
> struct vfio_dma *dma;
> bool do_accounting;
> + int contiguous_npage;
>
> if (!iommu || !user_pfn || !phys_pfn)
> return -EINVAL;
> @@ -663,7 +853,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> */
> do_accounting = !IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu);
>
> - for (i = 0; i < npage; i++) {
> + for (i = 0; i < npage; i += contiguous_npage) {
> dma_addr_t iova;
> struct vfio_pfn *vpfn;
>
> @@ -682,31 +872,18 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> vpfn = vfio_iova_get_vfio_pfn(dma, iova);
> if (vpfn) {
> phys_pfn[i] = vpfn->pfn;
> - continue;
> - }
> -
> - remote_vaddr = dma->vaddr + (iova - dma->iova);
> - ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn[i],
> - do_accounting);
> - if (ret)
> - goto pin_unwind;
> -
> - ret = vfio_add_to_pfn_list(dma, iova, phys_pfn[i]);
> - if (ret) {
> - if (put_pfn(phys_pfn[i], dma->prot) && do_accounting)
> - vfio_lock_acct(dma, -1, true);
> - goto pin_unwind;
> - }
> -
> - if (iommu->dirty_page_tracking) {
> - unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
> -
> - /*
> - * Bitmap populated with the smallest supported page
> - * size
> - */
> - bitmap_set(dma->bitmap,
> - (iova - dma->iova) >> pgshift, 1);
> + contiguous_npage = 1;
> + } else {
> + ret = vfio_get_contiguous_pages_length(dma,
> + &user_pfn[i], npage - i);
> + if (ret < 0)
> + goto pin_unwind;
> +
> + ret = vfio_iommu_type1_pin_contiguous_pages(iommu,
> + dma, &user_pfn[i], ret, &phys_pfn[i], do_accounting);
> + if (ret < 0)
> + goto pin_unwind;
> + contiguous_npage = ret;
> }
> }
> ret = i;
> --
> 2.19.1
> .
>
hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
vfio_pin_pages() accepts an array of unrelated iova pfns and processes
each to return the physical pfn. When dealing with large arrays of
contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
it is processed page by page. In this case, we can divide the iova pfn
array into multiple continuous ranges and optimize them. I have a set
of performance test data for reference.
The patch was not applied
1 page 512 pages
no huge pages： 1638ns 223651ns
THP： 1668ns 222330ns
HugeTLB： 1526ns 208151ns
The patch was applied
1 page 512 pages
no huge pages 1735ns 167286ns
THP： 1934ns 126900ns
HugeTLB： 1713ns 102188ns
As Alex Williamson said, this patch lacks proof that it works in the
real world. I think you will have some valuable opinions.
Regards,
Xu
On 12/9/20 6:54 AM, Cornelia Huck wrote:
> On Tue, 8 Dec 2020 21:55:53 +0800
> "xuxiaoyang (C)" <[email protected]> wrote:
>
>> On 2020/11/21 15:58, xuxiaoyang (C) wrote:
>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>> each to return the physical pfn. When dealing with large arrays of
>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>> it is processed page by page.In this case, we can divide the iova pfn
>>> array into multiple continuous ranges and optimize them. For example,
>>> when the iova pfn array is {1,5,6,7,9}, it will be divided into three
>>> groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
>>> number of calls to pin_user_pages_remote is reduced from 3 times to once.
>>> For single page or large array of discontinuous iovas, we still use
>>> vfio_pin_page_external to deal with it to reduce the performance loss
>>> caused by refactoring.
>>>
>>> Signed-off-by: Xiaoyang Xu <[email protected]>
>
> (...)
>
>>
>> hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
>>
>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>> each to return the physical pfn. When dealing with large arrays of
>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>> it is processed page by page. In this case, we can divide the iova pfn
>> array into multiple continuous ranges and optimize them. I have a set
>> of performance test data for reference.
>>
>> The patch was not applied
>> 1 page 512 pages
>> no huge pages： 1638ns 223651ns
>> THP： 1668ns 222330ns
>> HugeTLB： 1526ns 208151ns
>>
>> The patch was applied
>> 1 page 512 pages
>> no huge pages 1735ns 167286ns
>> THP： 1934ns 126900ns
>> HugeTLB： 1713ns 102188ns
>>
>> As Alex Williamson said, this patch lacks proof that it works in the
>> real world. I think you will have some valuable opinions.
>
> Looking at this from the vfio-ccw angle, I'm not sure how much this
> would buy us, as we deal with IDAWs, which are designed so that they
> can be non-contiguous. I guess this depends a lot on what the guest
> does.
This would be my concern too, but I don't have data off the top of my
head to say one way or another...
>
> Eric, any opinion? Do you maybe also happen to have a test setup that
> mimics workloads actually seen in the real world?
>
...I do have some test setups, which I will try to get some data from in
a couple days. At the moment I've broken most of those setups trying to
implement some other stuff, and can't revert back at the moment. Will
get back to this.
Eric
On Tue, 8 Dec 2020 21:55:53 +0800
"xuxiaoyang (C)" <[email protected]> wrote:
> On 2020/11/21 15:58, xuxiaoyang (C) wrote:
> > vfio_pin_pages() accepts an array of unrelated iova pfns and processes
> > each to return the physical pfn. When dealing with large arrays of
> > contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
> > it is processed page by page.In this case, we can divide the iova pfn
> > array into multiple continuous ranges and optimize them. For example,
> > when the iova pfn array is {1,5,6,7,9}, it will be divided into three
> > groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
> > number of calls to pin_user_pages_remote is reduced from 3 times to once.
> > For single page or large array of discontinuous iovas, we still use
> > vfio_pin_page_external to deal with it to reduce the performance loss
> > caused by refactoring.
> >
> > Signed-off-by: Xiaoyang Xu <[email protected]>
(...)
>
> hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
>
> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
> each to return the physical pfn. When dealing with large arrays of
> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
> it is processed page by page. In this case, we can divide the iova pfn
> array into multiple continuous ranges and optimize them. I have a set
> of performance test data for reference.
>
> The patch was not applied
> 1 page 512 pages
> no huge pages： 1638ns 223651ns
> THP： 1668ns 222330ns
> HugeTLB： 1526ns 208151ns
>
> The patch was applied
> 1 page 512 pages
> no huge pages 1735ns 167286ns
> THP： 1934ns 126900ns
> HugeTLB： 1713ns 102188ns
>
> As Alex Williamson said, this patch lacks proof that it works in the
> real world. I think you will have some valuable opinions.
Looking at this from the vfio-ccw angle, I'm not sure how much this
would buy us, as we deal with IDAWs, which are designed so that they
can be non-contiguous. I guess this depends a lot on what the guest
does.
Eric, any opinion? Do you maybe also happen to have a test setup that
mimics workloads actually seen in the real world?
On 2020/12/9 19:54, Cornelia Huck wrote:
> On Tue, 8 Dec 2020 21:55:53 +0800
> "xuxiaoyang (C)" <[email protected]> wrote:
>
>> On 2020/11/21 15:58, xuxiaoyang (C) wrote:
>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>> each to return the physical pfn. When dealing with large arrays of
>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>> it is processed page by page.In this case, we can divide the iova pfn
>>> array into multiple continuous ranges and optimize them. For example,
>>> when the iova pfn array is {1,5,6,7,9}, it will be divided into three
>>> groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
>>> number of calls to pin_user_pages_remote is reduced from 3 times to once.
>>> For single page or large array of discontinuous iovas, we still use
>>> vfio_pin_page_external to deal with it to reduce the performance loss
>>> caused by refactoring.
>>>
>>> Signed-off-by: Xiaoyang Xu <[email protected]>
>
> (...)
>
>>
>> hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
>>
>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>> each to return the physical pfn. When dealing with large arrays of
>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>> it is processed page by page. In this case, we can divide the iova pfn
>> array into multiple continuous ranges and optimize them. I have a set
>> of performance test data for reference.
>>
>> The patch was not applied
>> 1 page 512 pages
>> no huge pages： 1638ns 223651ns
>> THP： 1668ns 222330ns
>> HugeTLB： 1526ns 208151ns
>>
>> The patch was applied
>> 1 page 512 pages
>> no huge pages 1735ns 167286ns
>> THP： 1934ns 126900ns
>> HugeTLB： 1713ns 102188ns
>>
>> As Alex Williamson said, this patch lacks proof that it works in the
>> real world. I think you will have some valuable opinions.
>
> Looking at this from the vfio-ccw angle, I'm not sure how much this
> would buy us, as we deal with IDAWs, which are designed so that they
> can be non-contiguous. I guess this depends a lot on what the guest
> does.
>
> Eric, any opinion? Do you maybe also happen to have a test setup that
> mimics workloads actually seen in the real world?
>
> .
>
Thank you for your reply. The iova array constructed using
pfn_array_alloc is continuous, and I think there will be
some performance improvements here.
Regards,
Xu
On 2020/12/9 22:42, Eric Farman wrote:
>
>
> On 12/9/20 6:54 AM, Cornelia Huck wrote:
>> On Tue, 8 Dec 2020 21:55:53 +0800
>> "xuxiaoyang (C)" <[email protected]> wrote:
>>
>>> On 2020/11/21 15:58, xuxiaoyang (C) wrote:
>>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>>> each to return the physical pfn. When dealing with large arrays of
>>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>>> it is processed page by page.In this case, we can divide the iova pfn
>>>> array into multiple continuous ranges and optimize them. For example,
>>>> when the iova pfn array is {1,5,6,7,9}, it will be divided into three
>>>> groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
>>>> number of calls to pin_user_pages_remote is reduced from 3 times to once.
>>>> For single page or large array of discontinuous iovas, we still use
>>>> vfio_pin_page_external to deal with it to reduce the performance loss
>>>> caused by refactoring.
>>>>
>>>> Signed-off-by: Xiaoyang Xu <[email protected]>
>>
>> (...)
>>
>>>
>>> hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
>>>
>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>> each to return the physical pfn. When dealing with large arrays of
>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>> it is processed page by page. In this case, we can divide the iova pfn
>>> array into multiple continuous ranges and optimize them. I have a set
>>> of performance test data for reference.
>>>
>>> The patch was not applied
>>> 1 page 512 pages
>>> no huge pages： 1638ns 223651ns
>>> THP： 1668ns 222330ns
>>> HugeTLB： 1526ns 208151ns
>>>
>>> The patch was applied
>>> 1 page 512 pages
>>> no huge pages 1735ns 167286ns
>>> THP： 1934ns 126900ns
>>> HugeTLB： 1713ns 102188ns
>>>
>>> As Alex Williamson said, this patch lacks proof that it works in the
>>> real world. I think you will have some valuable opinions.
>>
>> Looking at this from the vfio-ccw angle, I'm not sure how much this
>> would buy us, as we deal with IDAWs, which are designed so that they
>> can be non-contiguous. I guess this depends a lot on what the guest
>> does.
>
> This would be my concern too, but I don't have data off the top of my head to say one way or another...
>
>>
>> Eric, any opinion? Do you maybe also happen to have a test setup that
>> mimics workloads actually seen in the real world?
>>
>
> ...I do have some test setups, which I will try to get some data from in a couple days. At the moment I've broken most of those setups trying to implement some other stuff, and can't revert back at the moment. Will get back to this.
>
> Eric
> .
Thank you for your reply. Looking forward to your test data.
Regards,
Xu
On 2020/12/15 2:58, Eric Farman wrote:
>
>
> On 12/10/20 8:56 AM, xuxiaoyang (C) wrote:
>>
>>
>> On 2020/12/9 22:42, Eric Farman wrote:
>>>
>>>
>>> On 12/9/20 6:54 AM, Cornelia Huck wrote:
>>>> On Tue, 8 Dec 2020 21:55:53 +0800
>>>> "xuxiaoyang (C)" <[email protected]> wrote:
>>>>
>>>>> On 2020/11/21 15:58, xuxiaoyang (C) wrote:
>>>>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>>>>> each to return the physical pfn. When dealing with large arrays of
>>>>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>>>>> it is processed page by page.In this case, we can divide the iova pfn
>>>>>> array into multiple continuous ranges and optimize them. For example,
>>>>>> when the iova pfn array is {1,5,6,7,9}, it will be divided into three
>>>>>> groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
>>>>>> number of calls to pin_user_pages_remote is reduced from 3 times to once.
>>>>>> For single page or large array of discontinuous iovas, we still use
>>>>>> vfio_pin_page_external to deal with it to reduce the performance loss
>>>>>> caused by refactoring.
>>>>>>
>>>>>> Signed-off-by: Xiaoyang Xu <[email protected]>
>>>>
>>>> (...)
>>>>
>>>>>
>>>>> hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
>>>>>
>>>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>>>> each to return the physical pfn. When dealing with large arrays of
>>>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>>>> it is processed page by page. In this case, we can divide the iova pfn
>>>>> array into multiple continuous ranges and optimize them. I have a set
>>>>> of performance test data for reference.
>>>>>
>>>>> The patch was not applied
>>>>> 1 page 512 pages
>>>>> no huge pages： 1638ns 223651ns
>>>>> THP： 1668ns 222330ns
>>>>> HugeTLB： 1526ns 208151ns
>>>>>
>>>>> The patch was applied
>>>>> 1 page 512 pages
>>>>> no huge pages 1735ns 167286ns
>>>>> THP： 1934ns 126900ns
>>>>> HugeTLB： 1713ns 102188ns
>>>>>
>>>>> As Alex Williamson said, this patch lacks proof that it works in the
>>>>> real world. I think you will have some valuable opinions.
>>>>
>>>> Looking at this from the vfio-ccw angle, I'm not sure how much this
>>>> would buy us, as we deal with IDAWs, which are designed so that they
>>>> can be non-contiguous. I guess this depends a lot on what the guest
>>>> does.
>>>
>>> This would be my concern too, but I don't have data off the top of my head to say one way or another...
>>>
>>>>
>>>> Eric, any opinion? Do you maybe also happen to have a test setup that
>>>> mimics workloads actually seen in the real world?
>>>>
>>>
>>> ...I do have some test setups, which I will try to get some data from in a couple days. At the moment I've broken most of those setups trying to implement some other stuff, and can't revert back at the moment. Will get back to this.
>>>
>>> Eric
>>> .
>>
>> Thank you for your reply. Looking forward to your test data.
>
> Xu,
>
> The scenario I ran was a host kernel 5.10.0-rc7 with qemu 5.2.0, with a Fedora 32 guest with 4 VCPU and 4GB memory. I tried this a handful of times across a couple different hosts, so the likelihood that these numbers are outliers are pretty low. The histograms below come from a simple bpftrace, recording the number of pages asked to be pinned, and the length of time (in nanoseconds) it took to pin all those pages. I separated out the length of time for a request of one page versus a request of multiple pages, because as you will see the former far outnumbers the latter.
>
> The first thing I tried was simply to boot the guest via vfio-ccw, to see how the patch itself behaved:
>
> @1_page_ns BASE +PATCH
> 256, 512 12531 42.50% 12744 42.26%
> 512, 1K 5660 19.20% 5611 18.61%
> 1K, 2K 8416 28.54% 8947 29.67%
> 2K, 4K 2694 9.14% 2669 8.85%
> 4K, 8K 164 0.56% 169 0.56%
> 8K, 16K 14 0.05% 14 0.05%
> 16K, 32K 2 0.01% 3 0.01%
> 32K, 64K 0 0.00% 0 0.00%
> 64K, 128K 0 0.00% 0 0.00%
>
> @n_pages_ns BASE +PATCH
> 256, 512 0 0.00% 0 0.00%
> 512, 1K 67 0.97% 48 0.68%
> 1K, 2K 1598 23.13% 1036 14.71%
> 2K, 4K 2784 40.30% 3112 44.17%
> 4K, 8K 1288 18.64% 1579 22.41%
> 8K, 16K 1011 14.63% 1032 14.65%
> 16K, 32K 159 2.30% 234 3.32%
> 32K, 64K 1 0.01% 2 0.03%
> 64K, 128K 0 0.00% 2 0.03%
>
> @npage BASE +PATCH
> 1 29484 81.02% 30157 81.06%
> 2, 4 3298 9.06% 3385 9.10%
> 4, 8 1011 2.78% 1029 2.77%
> 8, 16 2600 7.14% 2631 7.07%
>
>
> The second thing I tried was simply fio, running it for about 10 minutes with a few minutes each for sequential read, sequential write, random read, and random write. (I tried this with both the guest booted off vfio-ccw and virtio-blk, but the difference was negligible.) The results in this space are similar as well:
>
> @1_page_ns BASE +PATCH
> 256, 512 5648104 66.79% 6615878 66.75%
> 512, 1K 1784047 21.10% 2082852 21.01%
> 1K, 2K 648877 7.67% 771964 7.79%
> 2K, 4K 339551 4.01% 396381 4.00%
> 4K, 8K 32513 0.38% 40359 0.41%
> 8K, 16K 2602 0.03% 2884 0.03%
> 16K, 32K 758 0.01% 762 0.01%
> 32K, 64K 434 0.01% 352 0.00%
>
> @n_pages_ns BASE +PATCH
> 256, 512 0 0.00% 0 0.00%
> 512, 1K 470803 12.18% 360524 7.95%
> 1K, 2K 1305166 33.75% 1739183 38.37%
> 2K, 4K 1338277 34.61% 1471161 32.46%
> 4K, 8K 733480 18.97% 937341 20.68%
> 8K, 16K 16954 0.44% 20708 0.46%
> 16K, 32K 1278 0.03% 2197 0.05%
> 32K, 64K 707 0.02% 703 0.02%
>
> @npage BASE +PATCH
> 1 8457107 68.62% 9911624 68.62%
> 2, 4 2066957 16.77% 2446462 16.94%
> 4, 8 359989 2.92% 417188 2.89%
> 8, 16 1440006 11.68% 1668482 11.55%
>
>
> I tried a smattering of other tests that might be more realistic, but the results were all pretty similar so there's no point in appending them here. Across the board, the amount of time spent on a multi-page request grows with the supplied patch. It doesn't get me very excited.
>
> If you are wondering why this might be, Conny's initial take about IDAWs being non-contiguous by design is spot on. Let's observe the page counts given to vfio_iommu_type1_pin_contiguous_pages() in addition to the counts in vfio_iommu_type1_pin_pages(). The following is an example of one guest boot PLUS an fio run:
>
> vfio_iommu_type1_pin_pages npage:
> 1 9890332 68.64%
> 2, 4 2438213 16.92%
> 4, 8 416278 2.89%
> 8, 16 1663201 11.54%
> Total 14408024
>
> vfio_iommu_type1_pin_contiguous_pages npage:
> 1 16384925 86.89%
> 2, 4 1327548 7.04%
> 4, 8 727564 3.86%
> 8, 16 417182 2.21%
> Total 18857219
>
> Yup... 87% of the calls to vfio_iommu_type1_pin_contiguous_pages() do so with a length of just a single page.
>
> Happy to provide more data if desired, but it doesn't look like a benefit to vfio-ccw's use.
>
> Thanks,
> Eric
>
>
Eric, vfio-ccw pin single page accounted for 87%,
and the length of continuous pages is very short.
In my test data, the continuous page length is 512,
which is a huge difference. It is easy to understand
that this patch does not benefit vfio-ccw.
Finally, thank you very much for your test data.
Regards,
Xu
>>
>> Regards,
>> Xu
>>
> .