2022-05-03 01:23:28

by Vipin Sharma

Subject: [PATCH v2] KVM: x86/mmu: Speed up slot_rmap_walk_next for sparsely populated rmaps

Avoid calling handlers on empty rmap entries and skip to the next non
empty rmap entry.

Empty rmap entries are noop in handlers.

Signed-off-by: Vipin Sharma <[email protected]>
Suggested-by: Sean Christopherson <[email protected]>
---

v2:
- Removed noinline from slot_rmap_walk_next signature

v1:
- https://lore.kernel.org/lkml/[email protected]

arch/x86/kvm/mmu/mmu.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 77785587332e..4e8d546431eb 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1501,9 +1501,11 @@ static bool slot_rmap_walk_okay(struct slot_rmap_walk_iterator *iterator)

static void slot_rmap_walk_next(struct slot_rmap_walk_iterator *iterator)
{
- if (++iterator->rmap <= iterator->end_rmap) {
+ while (++iterator->rmap <= iterator->end_rmap) {
iterator->gfn += (1UL << KVM_HPAGE_GFN_SHIFT(iterator->level));
- return;
+
+ if (iterator->rmap->val)
+ return;
}

if (++iterator->level > iterator->end_level) {

base-commit: 71d7c575a673d42ad7175ad5fc27c85c80330311
--
2.36.0.464.gb9c8b46e94-goog

2022-05-03 11:14:18

by Paolo Bonzini

Subject: Re: [PATCH v2] KVM: x86/mmu: Speed up slot_rmap_walk_next for sparsely populated rmaps

On 5/3/22 00:03, Vipin Sharma wrote:
> Avoid calling handlers on empty rmap entries and skip to the next non
> empty rmap entry.
>
> Empty rmap entries are noop in handlers.
>
> Signed-off-by: Vipin Sharma <[email protected]>
> Suggested-by: Sean Christopherson <[email protected]>
> ---
>
> v2:
> - Removed noinline from slot_rmap_walk_next signature
>
> v1:
> - https://lore.kernel.org/lkml/[email protected]
>
> arch/x86/kvm/mmu/mmu.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 77785587332e..4e8d546431eb 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1501,9 +1501,11 @@ static bool slot_rmap_walk_okay(struct slot_rmap_walk_iterator *iterator)
>
> static void slot_rmap_walk_next(struct slot_rmap_walk_iterator *iterator)
> {
> - if (++iterator->rmap <= iterator->end_rmap) {
> + while (++iterator->rmap <= iterator->end_rmap) {
> iterator->gfn += (1UL << KVM_HPAGE_GFN_SHIFT(iterator->level));
> - return;
> +
> + if (iterator->rmap->val)
> + return;
> }
>
> if (++iterator->level > iterator->end_level) {
>
> base-commit: 71d7c575a673d42ad7175ad5fc27c85c80330311

Queued, thanks.

Paolo