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(bras-base-toroon474qw-grc-65-184-144-111-238.dsl.bell.ca. [184.144.111.238]) by smtp.gmail.com with ESMTPSA id l12sm1199651qtx.45.2021.07.30.15.05.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Jul 2021 15:05:04 -0700 (PDT) From: Peter Xu To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Vitaly Kuznetsov , Sean Christopherson , peterx@redhat.com, Maxim Levitsky , Paolo Bonzini Subject: [PATCH v3 5/7] KVM: X86: MMU: Tune PTE_LIST_EXT to be bigger Date: Fri, 30 Jul 2021 18:04:53 -0400 Message-Id: <20210730220455.26054-6-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210730220455.26054-1-peterx@redhat.com> References: <20210730220455.26054-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- arch/x86/kvm/mmu/mmu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 16c99f771c9e..c0b452bb5dd9 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 -/* 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]; -- 2.31.1