One comment on this one.
On Fri, Feb 2, 2024 at 4:56 PM David Hildenbrand <da...@redhat.com> wrote:
>
> Let's speed up GPA to memory region / virtual address lookup. Store the
> memory regions ordered by guest physical addresses, and use binary
> search for address translation, as well as when adding/removing memory
> regions.
>
> Most importantly, this will speed up GPA->VA address translation when we
> have many memslots.
>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> subprojects/libvhost-user/libvhost-user.c | 49 +++++++++++++++++++++--
> 1 file changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/subprojects/libvhost-user/libvhost-user.c
> b/subprojects/libvhost-user/libvhost-user.c
> index d036b54ed0..75e47b7bb3 100644
> --- a/subprojects/libvhost-user/libvhost-user.c
> +++ b/subprojects/libvhost-user/libvhost-user.c
> @@ -199,19 +199,30 @@ vu_panic(VuDev *dev, const char *msg, ...)
> static VuDevRegion *
> vu_gpa_to_mem_region(VuDev *dev, uint64_t guest_addr)
> {
> - unsigned int i;
> + int low = 0;
> + int high = dev->nregions - 1;
>
> /*
> * Memory regions cannot overlap in guest physical address space. Each
> * GPA belongs to exactly one memory region, so there can only be one
> * match.
> + *
> + * We store our memory regions ordered by GPA and can simply perform a
> + * binary search.
> */
> - for (i = 0; i < dev->nregions; i++) {
> - VuDevRegion *cur = &dev->regions[i];
> + while (low <= high) {
> + unsigned int mid = low + (high - low) / 2;
> + VuDevRegion *cur = &dev->regions[mid];
>
> if (guest_addr >= cur->gpa && guest_addr < cur->gpa + cur->size) {
> return cur;
> }
> + if (guest_addr >= cur->gpa + cur->size) {
> + low = mid + 1;
> + }
> + if (guest_addr < cur->gpa) {
> + high = mid - 1;
> + }
> }
> return NULL;
> }
> @@ -273,9 +284,14 @@ vu_remove_all_mem_regs(VuDev *dev)
> static void
> _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion *msg_region, int fd)
> {
> + const uint64_t start_gpa = msg_region->guest_phys_addr;
> + const uint64_t end_gpa = start_gpa + msg_region->memory_size;
> int prot = PROT_READ | PROT_WRITE;
> VuDevRegion *r;
> void *mmap_addr;
> + int low = 0;
> + int high = dev->nregions - 1;
> + unsigned int idx;
>
> DPRINT("Adding region %d\n", dev->nregions);
> DPRINT(" guest_phys_addr: 0x%016"PRIx64"\n",
> @@ -295,6 +311,29 @@ _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion
> *msg_region, int fd)
> prot = PROT_NONE;
> }
>
> + /*
> + * We will add memory regions into the array sorted by GPA. Perform a
> + * binary search to locate the insertion point: it will be at the low
> + * index.
> + */
> + while (low <= high) {
> + unsigned int mid = low + (high - low) / 2;
> + VuDevRegion *cur = &dev->regions[mid];
> +
> + /* Overlap of GPA addresses. */
Looks like this check will only catch if the new region is fully
contained within an existing region. I think we need to check whether
either start or end region are in the range, i.e.:
if ((start_gpa > curr_gpa && start_gpa < cur->gpa + curr_size ) ||
(end_gpa > currr->gpa && end_gpa < cur->gpa + curr->size) )
> + if (start_gpa < cur->gpa + cur->size && cur->gpa < end_gpa) {
> + vu_panic(dev, "regions with overlapping guest physical
> addresses");
> + return;
> + }
> + if (start_gpa >= cur->gpa + cur->size) {
> + low = mid + 1;
> + }
> + if (start_gpa < cur->gpa) {
> + high = mid - 1;
> + }
> + }
> + idx = low;
> +
> /*
> * We don't use offset argument of mmap() since the mapped address has
> * to be page aligned, and we use huge pages.
> @@ -308,7 +347,9 @@ _vu_add_mem_reg(VuDev *dev, VhostUserMemoryRegion
> *msg_region, int fd)
> DPRINT(" mmap_addr: 0x%016"PRIx64"\n",
> (uint64_t)(uintptr_t)mmap_addr);
>
> - r = &dev->regions[dev->nregions];
> + /* Shift all affected entries by 1 to open a hole at idx. */
> + r = &dev->regions[idx];
> + memmove(r + 1, r, sizeof(VuDevRegion) * (dev->nregions - idx));
> r->gpa = msg_region->guest_phys_addr;
> r->size = msg_region->memory_size;
> r->qva = msg_region->userspace_addr;
> --
> 2.43.0
>
>
