[PATCH v2 3/3] vfio/type1: Batch page pinning
From: Daniel Jordan
Date: Fri Feb 19 2021 - 11:14:50 EST
Pinning one 4K page at a time is inefficient, so do it in batches of 512
instead. This is just an optimization with no functional change
intended, and in particular the driver still calls iommu_map() with the
largest physically contiguous range possible.
Add two fields in vfio_batch to remember where to start between calls to
vfio_pin_pages_remote(), and use vfio_batch_unpin() to handle remaining
pages in the batch in case of error.
qemu pins pages for guests around 8% faster on my test system, a
two-node Broadwell server with 128G memory per node. The qemu process
was bound to one node with its allocations constrained there as well.
base test
guest ---------------- ----------------
mem (GB) speedup avg sec (std) avg sec (std)
1 7.4% 0.61 (0.00) 0.56 (0.00)
2 8.3% 0.93 (0.00) 0.85 (0.00)
4 8.4% 1.46 (0.00) 1.34 (0.00)
8 8.6% 2.54 (0.01) 2.32 (0.00)
16 8.3% 4.66 (0.00) 4.27 (0.01)
32 8.3% 8.94 (0.01) 8.20 (0.01)
64 8.2% 17.47 (0.01) 16.04 (0.03)
120 8.5% 32.45 (0.13) 29.69 (0.01)
perf diff confirms less time spent in pup. Here are the top ten
functions:
Baseline Delta Abs Symbol
78.63% +6.64% clear_page_erms
1.50% -1.50% __gup_longterm_locked
1.27% -0.78% __get_user_pages
+0.76% kvm_zap_rmapp.constprop.0
0.54% -0.53% vmacache_find
0.55% -0.51% get_pfnblock_flags_mask
0.48% -0.48% __get_user_pages_remote
+0.39% slot_rmap_walk_next
+0.32% vfio_pin_map_dma
+0.26% kvm_handle_hva_range
...
Suggested-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
drivers/vfio/vfio_iommu_type1.c | 135 +++++++++++++++++++++-----------
1 file changed, 89 insertions(+), 46 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index b7247a2fc87e..cec2083dd556 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -107,6 +107,8 @@ struct vfio_batch {
struct page **pages; /* for pin_user_pages_remote */
struct page *fallback_page; /* if pages alloc fails */
int capacity; /* length of pages array */
+ int size; /* of batch currently */
+ int offset; /* of next entry in pages */
};
struct vfio_group {
@@ -469,6 +471,9 @@ static int put_pfn(unsigned long pfn, int prot)
static void vfio_batch_init(struct vfio_batch *batch)
{
+ batch->size = 0;
+ batch->offset = 0;
+
if (unlikely(disable_hugepages))
goto fallback;
@@ -484,6 +489,17 @@ static void vfio_batch_init(struct vfio_batch *batch)
batch->capacity = 1;
}
+static void vfio_batch_unpin(struct vfio_batch *batch, struct vfio_dma *dma)
+{
+ while (batch->size) {
+ unsigned long pfn = page_to_pfn(batch->pages[batch->offset]);
+
+ put_pfn(pfn, dma->prot);
+ batch->offset++;
+ batch->size--;
+ }
+}
+
static void vfio_batch_fini(struct vfio_batch *batch)
{
if (batch->capacity == VFIO_BATCH_MAX_CAPACITY)
@@ -625,65 +641,88 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
long npage, unsigned long *pfn_base,
unsigned long limit, struct vfio_batch *batch)
{
- unsigned long pfn = 0;
+ unsigned long pfn;
+ struct mm_struct *mm = current->mm;
long ret, pinned = 0, lock_acct = 0;
bool rsvd;
dma_addr_t iova = vaddr - dma->vaddr + dma->iova;
/* This code path is only user initiated */
- if (!current->mm)
+ if (!mm)
return -ENODEV;
- ret = vaddr_get_pfns(current->mm, vaddr, 1, dma->prot, pfn_base,
- batch->pages);
- if (ret < 0)
- return ret;
-
- pinned++;
- rsvd = is_invalid_reserved_pfn(*pfn_base);
-
- /*
- * Reserved pages aren't counted against the user, externally pinned
- * pages are already counted against the user.
- */
- if (!rsvd && !vfio_find_vpfn(dma, iova)) {
- if (!dma->lock_cap && current->mm->locked_vm + 1 > limit) {
- put_pfn(*pfn_base, dma->prot);
- pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n", __func__,
- limit << PAGE_SHIFT);
- return -ENOMEM;
- }
- lock_acct++;
+ if (batch->size) {
+ /* Leftover pages in batch from an earlier call. */
+ *pfn_base = page_to_pfn(batch->pages[batch->offset]);
+ pfn = *pfn_base;
+ rsvd = is_invalid_reserved_pfn(*pfn_base);
+ } else {
+ *pfn_base = 0;
}
- if (unlikely(disable_hugepages))
- goto out;
+ while (npage) {
+ if (!batch->size) {
+ /* Empty batch, so refill it. */
+ long req_pages = min_t(long, npage, batch->capacity);
- /* Lock all the consecutive pages from pfn_base */
- for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
- pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
- ret = vaddr_get_pfns(current->mm, vaddr, 1, dma->prot, &pfn,
- batch->pages);
- if (ret < 0)
- break;
+ ret = vaddr_get_pfns(mm, vaddr, req_pages, dma->prot,
+ &pfn, batch->pages);
+ if (ret < 0)
+ goto unpin_out;
- if (pfn != *pfn_base + pinned ||
- rsvd != is_invalid_reserved_pfn(pfn)) {
- put_pfn(pfn, dma->prot);
- break;
+ batch->size = ret;
+ batch->offset = 0;
+
+ if (!*pfn_base) {
+ *pfn_base = pfn;
+ rsvd = is_invalid_reserved_pfn(*pfn_base);
+ }
}
- if (!rsvd && !vfio_find_vpfn(dma, iova)) {
- if (!dma->lock_cap &&
- current->mm->locked_vm + lock_acct + 1 > limit) {
- put_pfn(pfn, dma->prot);
- pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
- __func__, limit << PAGE_SHIFT);
- ret = -ENOMEM;
- goto unpin_out;
+ /*
+ * pfn is preset for the first iteration of this inner loop and
+ * updated at the end to handle a VM_PFNMAP pfn. In that case,
+ * batch->pages isn't valid (there's no struct page), so allow
+ * batch->pages to be touched only when there's more than one
+ * pfn to check, which guarantees the pfns are from a
+ * !VM_PFNMAP vma.
+ */
+ while (true) {
+ if (pfn != *pfn_base + pinned ||
+ rsvd != is_invalid_reserved_pfn(pfn))
+ goto out;
+
+ /*
+ * Reserved pages aren't counted against the user,
+ * externally pinned pages are already counted against
+ * the user.
+ */
+ if (!rsvd && !vfio_find_vpfn(dma, iova)) {
+ if (!dma->lock_cap &&
+ mm->locked_vm + lock_acct + 1 > limit) {
+ pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
+ __func__, limit << PAGE_SHIFT);
+ ret = -ENOMEM;
+ goto unpin_out;
+ }
+ lock_acct++;
}
- lock_acct++;
+
+ pinned++;
+ npage--;
+ vaddr += PAGE_SIZE;
+ iova += PAGE_SIZE;
+ batch->offset++;
+ batch->size--;
+
+ if (!batch->size)
+ break;
+
+ pfn = page_to_pfn(batch->pages[batch->offset]);
}
+
+ if (unlikely(disable_hugepages))
+ break;
}
out:
@@ -691,10 +730,11 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
unpin_out:
if (ret < 0) {
- if (!rsvd) {
+ if (pinned && !rsvd) {
for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
put_pfn(pfn, dma->prot);
}
+ vfio_batch_unpin(batch, dma);
return ret;
}
@@ -1453,6 +1493,7 @@ static int vfio_pin_map_dma(struct vfio_iommu *iommu, struct vfio_dma *dma,
if (ret) {
vfio_unpin_pages_remote(dma, iova + dma->size, pfn,
npage, true);
+ vfio_batch_unpin(&batch, dma);
break;
}
@@ -1716,11 +1757,13 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
ret = iommu_map(domain->domain, iova, phys,
size, dma->prot | domain->prot);
if (ret) {
- if (!dma->iommu_mapped)
+ if (!dma->iommu_mapped) {
vfio_unpin_pages_remote(dma, iova,
phys >> PAGE_SHIFT,
size >> PAGE_SHIFT,
true);
+ vfio_batch_unpin(&batch, dma);
+ }
goto unwind;
}
--
2.30.1