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Date: Fri, 7 Feb 2020 10:03:04 -0800
From: Davidlohr Bueso <dave@...olabs.net>
To: akpm@...ux-foundation.org
Cc: dave@...olabs.net, linux-kernel@...r.kernel.org, mcgrof@...nel.org,
broonie@...nel.org, alex.williamson@...hat.com, cohuck@...hat.com,
kvm@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 4/5] vfio/type1: optimize dma_list tree iterations
Both ->release() and ->attach_group() vfio_iommu driver
callbacks can incur in full in-order iommu->dma_list traversals,
which can be suboptimal under regular rbtree interators. This
patch proposes using the optimized llrbtree interface such that
we always have a branchless O(1) next node available. The cost
is higher memory footprint, mainly enlarging struct vfio_dma
by two pointers. This allows for minimal runtime overhead
when doing tree modifications.
Cc: alex.williamson@...hat.com
Cc: cohuck@...hat.com
Cc: kvm@...r.kernel.org
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
drivers/vfio/vfio_iommu_type1.c | 50 +++++++++++++++++++++++------------------
1 file changed, 28 insertions(+), 22 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 2ada8e6cdb88..875170fc8515 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -28,6 +28,7 @@
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/rbtree.h>
+#include <linux/ll_rbtree.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/slab.h>
@@ -65,7 +66,7 @@ struct vfio_iommu {
struct list_head iova_list;
struct vfio_domain *external_domain; /* domain for external user */
struct mutex lock;
- struct rb_root dma_list;
+ struct llrb_root dma_list;
struct blocking_notifier_head notifier;
unsigned int dma_avail;
bool v2;
@@ -81,7 +82,7 @@ struct vfio_domain {
};
struct vfio_dma {
- struct rb_node node;
+ struct llrb_node node;
dma_addr_t iova; /* Device address */
unsigned long vaddr; /* Process virtual addr */
size_t size; /* Map size (bytes) */
@@ -134,10 +135,10 @@ static int put_pfn(unsigned long pfn, int prot);
static struct vfio_dma *vfio_find_dma(struct vfio_iommu *iommu,
dma_addr_t start, size_t size)
{
- struct rb_node *node = iommu->dma_list.rb_node;
+ struct rb_node *node = iommu->dma_list.rb_root.rb_node;
while (node) {
- struct vfio_dma *dma = rb_entry(node, struct vfio_dma, node);
+ struct vfio_dma *dma = llrb_entry(node, struct vfio_dma, node);
if (start + size <= dma->iova)
node = node->rb_left;
@@ -152,26 +153,30 @@ static struct vfio_dma *vfio_find_dma(struct vfio_iommu *iommu,
static void vfio_link_dma(struct vfio_iommu *iommu, struct vfio_dma *new)
{
- struct rb_node **link = &iommu->dma_list.rb_node, *parent = NULL;
+ struct rb_node **link = &iommu->dma_list.rb_root.rb_node;
+ struct rb_node *parent = NULL;
+ struct llrb_node *prev = NULL;
struct vfio_dma *dma;
while (*link) {
parent = *link;
- dma = rb_entry(parent, struct vfio_dma, node);
+ dma = llrb_entry(parent, struct vfio_dma, node);
if (new->iova + new->size <= dma->iova)
link = &(*link)->rb_left;
- else
+ else {
link = &(*link)->rb_right;
+ prev = llrb_from_rb(parent);
+ }
}
- rb_link_node(&new->node, parent, link);
- rb_insert_color(&new->node, &iommu->dma_list);
+ rb_link_node(&new->node.rb_node, parent, link);
+ llrb_insert(&iommu->dma_list, &new->node, prev);
}
static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old)
{
- rb_erase(&old->node, &iommu->dma_list);
+ llrb_erase(&old->node, &iommu->dma_list);
}
/*
@@ -1170,15 +1175,15 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
struct vfio_domain *domain)
{
struct vfio_domain *d;
- struct rb_node *n;
+ struct llrb_node *n;
unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
int ret;
/* Arbitrarily pick the first domain in the list for lookups */
d = list_first_entry(&iommu->domain_list, struct vfio_domain, next);
- n = rb_first(&iommu->dma_list);
+ n = llrb_first(&iommu->dma_list);
- for (; n; n = rb_next(n)) {
+ for (; n; n = llrb_next(n)) {
struct vfio_dma *dma;
dma_addr_t iova;
@@ -1835,18 +1840,19 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
static void vfio_iommu_unmap_unpin_all(struct vfio_iommu *iommu)
{
- struct rb_node *node;
+ struct llrb_node *node;
- while ((node = rb_first(&iommu->dma_list)))
+ while ((node = llrb_first(&iommu->dma_list)))
vfio_remove_dma(iommu, rb_entry(node, struct vfio_dma, node));
}
static void vfio_iommu_unmap_unpin_reaccount(struct vfio_iommu *iommu)
{
- struct rb_node *n, *p;
+ struct llrb_node *n;
+ struct rb_node *p;
- n = rb_first(&iommu->dma_list);
- for (; n; n = rb_next(n)) {
+ n = llrb_first(&iommu->dma_list);
+ for (; n; n = llrb_next(n)) {
struct vfio_dma *dma;
long locked = 0, unlocked = 0;
@@ -1866,10 +1872,10 @@ static void vfio_iommu_unmap_unpin_reaccount(struct vfio_iommu *iommu)
static void vfio_sanity_check_pfn_list(struct vfio_iommu *iommu)
{
- struct rb_node *n;
+ struct llrb_node *n;
- n = rb_first(&iommu->dma_list);
- for (; n; n = rb_next(n)) {
+ n = llrb_first(&iommu->dma_list);
+ for (; n; n = llrb_next(n)) {
struct vfio_dma *dma;
dma = rb_entry(n, struct vfio_dma, node);
@@ -2060,7 +2066,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
INIT_LIST_HEAD(&iommu->domain_list);
INIT_LIST_HEAD(&iommu->iova_list);
- iommu->dma_list = RB_ROOT;
+ iommu->dma_list = LLRB_ROOT;
iommu->dma_avail = dma_entry_limit;
mutex_init(&iommu->lock);
BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
--
2.16.4
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