On 04.02.24 23:07, Raphael Norwitz wrote:
On Sun, Feb 4, 2024 at 9:51 AM David Hildenbrand <da...@redhat.com> wrote:
On 04.02.24 03:10, Raphael Norwitz wrote:
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.:
That check should cover all cases of overlaps, not just fully contained.
See the QEMU implementation of range_overlaps_rang() that contains a
similar logic:
return !(range2->upb < range1->lob || range1->upb < range2->lob);
!(range2->upb < range1->lob || range1->upb < range2->lob);
= !(range2->upb < range1->lob) && !(range1->upb < range2->lob)
= range2->upb >= range1->lob && range1->upb >= range2->lob
= range1->lob <= range2->upb && range2->lob <= range1->upb
In QEMU, upb is inclusive, if it were exclusive (like we have here):
= range1->lob < range2->upb && range2->lob < range1->upb
Which is what we have here with:
range1->lob = start_gpa
range1->upb = end_gpa
range2->lob = cur->gpa
range2->upb = cur->gpa + cur->size
Also if you are interested, see
https://stackoverflow.com/questions/3269434/whats-the-most-efficient-way-to-test-if-two-ranges-overlap
Thanks!
Got it, thanks for the full explanation. With that:
Reviewed-by: Raphael Norwitz <raph...@enfabrica.net>
Thanks!
--
Cheers,
David / dhildenb
