Messages in this thread | | | Subject | Re: [RFC PATCH 0/4] KVM: arm64: Improve efficiency of stage2 page table | From | "wangyanan (Y)" <> | Date | Wed, 24 Feb 2021 10:35:07 +0800 |
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Hi Alex,
On 2021/2/23 23:55, Alexandru Elisei wrote: > Hi Yanan, > > I wanted to review the patches, but unfortunately I get an error when trying to > apply the first patch in the series: > > Applying: KVM: arm64: Move the clean of dcache to the map handler > error: patch failed: arch/arm64/kvm/hyp/pgtable.c:464 > error: arch/arm64/kvm/hyp/pgtable.c: patch does not apply > error: patch failed: arch/arm64/kvm/mmu.c:882 > error: arch/arm64/kvm/mmu.c: patch does not apply > Patch failed at 0001 KVM: arm64: Move the clean of dcache to the map handler > hint: Use 'git am --show-current-patch=diff' to see the failed patch > When you have resolved this problem, run "git am --continue". > If you prefer to skip this patch, run "git am --skip" instead. > To restore the original branch and stop patching, run "git am --abort". > > Tried this with Linux tags v5.11-rc1 to v5.11-rc7. It looks like pgtable.c and > mmu.c from your patch is different than what is found on upstream master. Did you > use another branch as the base for your patches? Thanks for your attention. Indeed, this series was more or less based on the patches I post before (Link: https://lore.kernel.org/r/20210114121350.123684-4-wangyanan55@huawei.com). And they have already been merged into up-to-data upstream master (commit: 509552e65ae8287178a5cdea2d734dcd2d6380ab), but not into tags v5.11-rc1 to v5.11-rc7. Could you please try the newest upstream master(since commit: 509552e65ae8287178a5cdea2d734dcd2d6380ab) ? I have tested on my local and no apply errors occur.
Thanks,
Yanan.
> Thanks, > > Alex > > On 2/8/21 11:22 AM, Yanan Wang wrote: >> Hi, >> >> This series makes some efficiency improvement of stage2 page table code, >> and there are some test results to present the performance changes, which >> were tested by a kvm selftest [1] that I have post: >> [1] https://lore.kernel.org/lkml/20210208090841.333724-1-wangyanan55@huawei.com/ >> >> About patch 1: >> We currently uniformly clean dcache in user_mem_abort() before calling the >> fault handlers, if we take a translation fault and the pfn is cacheable. >> But if there are concurrent translation faults on the same page or block, >> clean of dcache for the first time is necessary while the others are not. >> >> By moving clean of dcache to the map handler, we can easily identify the >> conditions where CMOs are really needed and avoid the unnecessary ones. >> As it's a time consuming process to perform CMOs especially when flushing >> a block range, so this solution reduces much load of kvm and improve the >> efficiency of creating mappings. >> >> Test results: >> (1) when 20 vCPUs concurrently access 20G ram (all 1G hugepages): >> KVM create block mappings time: 52.83s -> 3.70s >> KVM recover block mappings time(after dirty-logging): 52.0s -> 2.87s >> >> (2) when 40 vCPUs concurrently access 20G ram (all 1G hugepages): >> KVM creating block mappings time: 104.56s -> 3.70s >> KVM recover block mappings time(after dirty-logging): 103.93s -> 2.96s >> >> About patch 2, 3: >> When KVM needs to coalesce the normal page mappings into a block mapping, >> we currently invalidate the old table entry first followed by invalidation >> of TLB, then unmap the page mappings, and install the block entry at last. >> >> It will cost a lot of time to unmap the numerous page mappings, which means >> the table entry will be left invalid for a long time before installation of >> the block entry, and this will cause many spurious translation faults. >> >> So let's quickly install the block entry at first to ensure uninterrupted >> memory access of the other vCPUs, and then unmap the page mappings after >> installation. This will reduce most of the time when the table entry is >> invalid, and avoid most of the unnecessary translation faults. >> >> Test results based on patch 1: >> (1) when 20 vCPUs concurrently access 20G ram (all 1G hugepages): >> KVM recover block mappings time(after dirty-logging): 2.87s -> 0.30s >> >> (2) when 40 vCPUs concurrently access 20G ram (all 1G hugepages): >> KVM recover block mappings time(after dirty-logging): 2.96s -> 0.35s >> >> So combined with patch 1, it makes a big difference of KVM creating mappings >> and recovering block mappings with not much code change. >> >> About patch 4: >> A new method to distinguish cases of memcache allocations is introduced. >> By comparing fault_granule and vma_pagesize, cases that require allocations >> from memcache and cases that don't can be distinguished completely. >> >> --- >> >> Details of test results >> platform: HiSilicon Kunpeng920 (FWB not supported) >> host kernel: Linux mainline (v5.11-rc6) >> >> (1) performance change of patch 1 >> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 20 >> (20 vcpus, 20G memory, block mappings(granule 1G)) >> Before patch: KVM_CREATE_MAPPINGS: 52.8338s 52.8327s 52.8336s 52.8255s 52.8303s >> After patch: KVM_CREATE_MAPPINGS: 3.7022s 3.7031s 3.7028s 3.7012s 3.7024s >> >> Before patch: KVM_ADJUST_MAPPINGS: 52.0466s 52.0473s 52.0550s 52.0518s 52.0467s >> After patch: KVM_ADJUST_MAPPINGS: 2.8787s 2.8781s 2.8785s 2.8742s 2.8759s >> >> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 40 >> (40 vcpus, 20G memory, block mappings(granule 1G)) >> Before patch: KVM_CREATE_MAPPINGS: 104.560s 104.556s 104.554s 104.556s 104.550s >> After patch: KVM_CREATE_MAPPINGS: 3.7011s 3.7103s 3.7005s 3.7024s 3.7106s >> >> Before patch: KVM_ADJUST_MAPPINGS: 103.931s 103.936s 103.927s 103.942s 103.927s >> After patch: KVM_ADJUST_MAPPINGS: 2.9621s 2.9648s 2.9474s 2.9587s 2.9603s >> >> (2) performance change of patch 2, 3(based on patch 1) >> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 1 >> (1 vcpu, 20G memory, block mappings(granule 1G)) >> Before patch: KVM_ADJUST_MAPPINGS: 2.8241s 2.8234s 2.8245s 2.8230s 2.8652s >> After patch: KVM_ADJUST_MAPPINGS: 0.2444s 0.2442s 0.2423s 0.2441s 0.2429s >> >> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 20 >> (20 vcpus, 20G memory, block mappings(granule 1G)) >> Before patch: KVM_ADJUST_MAPPINGS: 2.8787s 2.8781s 2.8785s 2.8742s 2.8759s >> After patch: KVM_ADJUST_MAPPINGS: 0.3008s 0.3004s 0.2974s 0.2917s 0.2900s >> >> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 40 >> (40 vcpus, 20G memory, block mappings(granule 1G)) >> Before patch: KVM_ADJUST_MAPPINGS: 2.9621s 2.9648s 2.9474s 2.9587s 2.9603s >> After patch: KVM_ADJUST_MAPPINGS: 0.3541s 0.3694s 0.3656s 0.3693s 0.3687s >> >> --- >> >> Yanan Wang (4): >> KVM: arm64: Move the clean of dcache to the map handler >> KVM: arm64: Add an independent API for coalescing tables >> KVM: arm64: Install the block entry before unmapping the page mappings >> KVM: arm64: Distinguish cases of memcache allocations completely >> >> arch/arm64/include/asm/kvm_mmu.h | 16 ------- >> arch/arm64/kvm/hyp/pgtable.c | 82 +++++++++++++++++++++----------- >> arch/arm64/kvm/mmu.c | 39 ++++++--------- >> 3 files changed, 69 insertions(+), 68 deletions(-) >> > .
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