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vhost: use binary search instead of linear in find_region() 

For default region layouts performance stays the same
as linear search i.e. it takes around 210ns average for
translate_desc() that inlines find_region().

But it scales better with larger amount of regions,
235ns BS vs 300ns LS with 55 memory regions
and it will be about the same values when allowed number
of slots is increased to 509 like it has been done in kvm.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Igor Mammedov 2015-06-16 18:33:35 +02:00 committed by Michael S. Tsirkin
parent 8b0a9d4230
commit bcfeacab45
1 changed files with 28 additions and 10 deletions
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38
drivers/vhost/vhost.c
View File

@ -25,6 +25,7 @@
#include <linux/kthread.h>
#include <linux/cgroup.h>
#include <linux/module.h>
#include <linux/sort.h>
#include "vhost.h"
@ -663,6 +664,16 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq)
}
EXPORT_SYMBOL_GPL(vhost_vq_access_ok);
static int vhost_memory_reg_sort_cmp(const void *p1, const void *p2)
{
const struct vhost_memory_region *r1 = p1, *r2 = p2;
if (r1->guest_phys_addr < r2->guest_phys_addr)
return 1;
if (r1->guest_phys_addr > r2->guest_phys_addr)
return -1;
return 0;
}
static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
{
struct vhost_memory mem, *newmem, *oldmem;
@ -682,9 +693,11 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
memcpy(newmem, &mem, size);
if (copy_from_user(newmem->regions, m->regions,
mem.nregions * sizeof *m->regions)) {
kfree(newmem);
kvfree(newmem);
return -EFAULT;
}
sort(newmem->regions, newmem->nregions, sizeof(*newmem->regions),
vhost_memory_reg_sort_cmp, NULL);
if (!memory_access_ok(d, newmem, 0)) {
kfree(newmem);
@ -992,17 +1005,22 @@ EXPORT_SYMBOL_GPL(vhost_dev_ioctl);
static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
__u64 addr, __u32 len)
{
struct vhost_memory_region *reg;
int i;
const struct vhost_memory_region *reg;
int start = 0, end = mem->nregions;
/* linear search is not brilliant, but we really have on the order of 6
* regions in practice */
for (i = 0; i < mem->nregions; ++i) {
reg = mem->regions + i;
if (reg->guest_phys_addr <= addr &&
reg->guest_phys_addr + reg->memory_size - 1 >= addr)
return reg;
while (start < end) {
int slot = start + (end - start) / 2;
reg = mem->regions + slot;
if (addr >= reg->guest_phys_addr)
end = slot;
else
start = slot + 1;
}
reg = mem->regions + start;
if (addr >= reg->guest_phys_addr &&
reg->guest_phys_addr + reg->memory_size > addr)
return reg;
return NULL;
}