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| author |  Peter Xu <peterx@redhat.com>
| 2021-07-30 18:04:53 -0400 |
|---|---|---|
| committer |  Paolo Bonzini <pbonzini@redhat.com>
| 2021-08-04 05:55:56 -0400 |
| commit | dc1cff969101afd08601e90463b44bd572e62dd4 (patch) | |
| tree | 73213286ccce4ee229b90b7d432c169964190368 | |
| parent | KVM: const-ify all relevant uses of struct kvm_memory_slot (diff) | |
| download | linux-dc1cff969101afd08601e90463b44bd572e62dd4.tar.gz linux-dc1cff969101afd08601e90463b44bd572e62dd4.tar.bz2 linux-dc1cff969101afd08601e90463b44bd572e62dd4.zip | |
KVM: X86: MMU: Tune PTE_LIST_EXT to be bigger
Currently rmap array element only contains 3 entries. However for EPT=N there
could have a lot of guest pages that got tens of even hundreds of rmap entry.
A normal distribution of a 6G guest (even if idle) shows this with rmap count
statistics:
Rmap_Count: 0 1 2-3 4-7 8-15 16-31 32-63 64-127 128-255 256-511 512-1023
Level=4K: 3089171 49005 14016 1363 235 212 15 7 0 0 0
Level=2M: 5951 227 0 0 0 0 0 0 0 0 0
Level=1G: 32 0 0 0 0 0 0 0 0 0 0
If we do some more fork some pages will grow even larger rmap counts.
This patch makes PTE_LIST_EXT bigger so it'll be more efficient for the general
use case of EPT=N as we do list reference less and the loops over PTE_LIST_EXT
will be slightly more efficient; but still not too large so less waste when
array not full.
It should not affecting EPT=Y since EPT normally only has zero or one rmap
entry for each page, so no array is even allocated.
With a test case to fork 500 child and recycle them ("./rmap_fork 500" [1]),
this patch speeds up fork time of about 29%.
Before: 473.90 (+-5.93%)
After: 366.10 (+-4.94%)
[1] https://github.com/xzpeter/clibs/commit/825436f825453de2ea5aaee4bdb1c92281efe5b3
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220455.26054-6-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | arch/x86/kvm/mmu/mmu.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index e702361b4409..69ad8189d7eb 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -137,8 +137,8 @@ module_param(dbg, bool, 0644); #include <trace/events/kvm.h> -/* make pte_list_desc fit well in cache line */ -#define PTE_LIST_EXT 3 +/* make pte_list_desc fit well in cache lines */ +#define PTE_LIST_EXT 15 struct pte_list_desc { u64 *sptes[PTE_LIST_EXT]; |