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vhost: optimize out no-change assignment 

Cirrus VGA (at least) calls register memory region
with the same values again and again. The
registration in vhost-net slows this a lot,
optimize by checking that the same data is already registered.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2011-03-31 15:45:51 +02:00
parent f5a4e64f8e
commit 4e789564d3
1 changed files with 54 additions and 0 deletions
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54
hw/vhost.c
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@ -297,6 +297,45 @@ static int vhost_verify_ring_mappings(struct vhost_dev *dev,
return 0;
}
static struct vhost_memory_region *vhost_dev_find_reg(struct vhost_dev *dev,
uint64_t start_addr,
uint64_t size)
{
int i, n = dev->mem->nregions;
for (i = 0; i < n; ++i) {
struct vhost_memory_region *reg = dev->mem->regions + i;
if (ranges_overlap(reg->guest_phys_addr, reg->memory_size,
start_addr, size)) {
return reg;
}
}
return NULL;
}
static bool vhost_dev_cmp_memory(struct vhost_dev *dev,
uint64_t start_addr,
uint64_t size,
uint64_t uaddr)
{
struct vhost_memory_region *reg = vhost_dev_find_reg(dev, start_addr, size);
uint64_t reglast;
uint64_t memlast;
if (!reg) {
return true;
}
reglast = range_get_last(reg->guest_phys_addr, reg->memory_size);
memlast = range_get_last(start_addr, size);
/* Need to extend region? */
if (start_addr < reg->guest_phys_addr || memlast > reglast) {
return true;
}
/* userspace_addr changed? */
return uaddr != reg->userspace_addr + start_addr - reg->guest_phys_addr;
}
static void vhost_client_set_memory(CPUPhysMemoryClient *client,
target_phys_addr_t start_addr,
ram_addr_t size,
@ -309,6 +348,7 @@ static void vhost_client_set_memory(CPUPhysMemoryClient *client,
(dev->mem->nregions + 1) * sizeof dev->mem->regions[0];
uint64_t log_size;
int r;
dev->mem = qemu_realloc(dev->mem, s);
if (log_dirty) {
@ -317,6 +357,20 @@ static void vhost_client_set_memory(CPUPhysMemoryClient *client,
assert(size);
/* Optimize no-change case. At least cirrus_vga does this a lot at this time. */
if (flags == IO_MEM_RAM) {
if (!vhost_dev_cmp_memory(dev, start_addr, size,
(uintptr_t)qemu_get_ram_ptr(phys_offset))) {
/* Region exists with same address. Nothing to do. */
return;
}
} else {
if (!vhost_dev_find_reg(dev, start_addr, size)) {
/* Removing region that we don't access. Nothing to do. */
return;
}
}
vhost_dev_unassign_memory(dev, start_addr, size);
if (flags == IO_MEM_RAM) {
/* Add given mapping, merging adjacent regions if any */