Re: [RFC PATCH 0/4] KVM: arm64: Improve efficiency of stage2 page table
From: Alexandru Elisei
Date: Wed Feb 24 2021 - 12:21:51 EST
Hi,
On 2/24/21 2:35 AM, wangyanan (Y) wrote:
>
Hi Alex,
>
>
On 2021年2月23日 23:55, Alexandru Elisei wrote:
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> 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:
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https://lore.kernel.org/r/20210114121350.123684-4-wangyanan55@xxxxxxxxxx).
>
And they have already been merged into up-to-data upstream master (commit:
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509552e65ae8287178a5cdea2d734dcd2d6380ab), but not into tags v5.11-rc1 to
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v5.11-rc7.
>
Could you please try the newest upstream master(since commit:
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509552e65ae8287178a5cdea2d734dcd2d6380ab) ? I have tested on my local and no
>
apply errors occur.
That worked for me, thank you for the quick reply.
Just to double check, when you run the benchmarks, the before results are for a
kernel built from commit 509552e65ae8 ("KVM: arm64: Mark the page dirty only if
the fault is handled successfully"), and the after results are with this series on
top, right?
Thanks,
Alex
>
>
Thanks,
>
>
Yanan.
>
>
> Thanks,
>
>
>
> Alex
>
>
>
> On 2/8/21 11:22 AM, Yanan Wang wrote:
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>> 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:
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>> [1] https://lore.kernel.org/lkml/20210208090841.333724-1-wangyanan55@xxxxxxxxxx/
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>>
>
>> About patch 1:
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>> We currently uniformly clean dcache in user_mem_abort() before calling the
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>> fault handlers, if we take a translation fault and the pfn is cacheable.
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>> But if there are concurrent translation faults on the same page or block,
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>> clean of dcache for the first time is necessary while the others are not.
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>>
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>> By moving clean of dcache to the map handler, we can easily identify the
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>> conditions where CMOs are really needed and avoid the unnecessary ones.
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>> As it's a time consuming process to perform CMOs especially when flushing
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>> a block range, so this solution reduces much load of kvm and improve the
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>> efficiency of creating mappings.
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>>
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>> Test results:
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>> (1) when 20 vCPUs concurrently access 20G ram (all 1G hugepages):
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>> KVM create block mappings time: 52.83s -> 3.70s
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>> KVM recover block mappings time(after dirty-logging): 52.0s -> 2.87s
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>>
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>> (2) when 40 vCPUs concurrently access 20G ram (all 1G hugepages):
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>> KVM creating block mappings time: 104.56s -> 3.70s
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>> KVM recover block mappings time(after dirty-logging): 103.93s -> 2.96s
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>>
>
>> About patch 2, 3:
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>> When KVM needs to coalesce the normal page mappings into a block mapping,
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>> we currently invalidate the old table entry first followed by invalidation
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>> of TLB, then unmap the page mappings, and install the block entry at last.
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>>
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>> It will cost a lot of time to unmap the numerous page mappings, which means
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>> the table entry will be left invalid for a long time before installation of
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>> the block entry, and this will cause many spurious translation faults.
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>>
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>> So let's quickly install the block entry at first to ensure uninterrupted
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>> memory access of the other vCPUs, and then unmap the page mappings after
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>> installation. This will reduce most of the time when the table entry is
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>> invalid, and avoid most of the unnecessary translation faults.
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>>
>
>> Test results based on patch 1:
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>> (1) when 20 vCPUs concurrently access 20G ram (all 1G hugepages):
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>> KVM recover block mappings time(after dirty-logging): 2.87s -> 0.30s
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>>
>
>> (2) when 40 vCPUs concurrently access 20G ram (all 1G hugepages):
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>> KVM recover block mappings time(after dirty-logging): 2.96s -> 0.35s
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>>
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>> So combined with patch 1, it makes a big difference of KVM creating mappings
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>> and recovering block mappings with not much code change.
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>>
>
>> About patch 4:
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>> A new method to distinguish cases of memcache allocations is introduced.
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>> By comparing fault_granule and vma_pagesize, cases that require allocations
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>> from memcache and cases that don't can be distinguished completely.
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>>
>
>> ---
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>>
>
>> Details of test results
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>> platform: HiSilicon Kunpeng920 (FWB not supported)
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>> host kernel: Linux mainline (v5.11-rc6)
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>>
>
>> (1) performance change of patch 1
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>> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 20
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>> (20 vcpus, 20G memory, block mappings(granule 1G))
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>> 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
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>>
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>> Before patch: KVM_ADJUST_MAPPINGS: 52.0466s 52.0473s 52.0550s 52.0518s 52.0467s
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>> After patch: KVM_ADJUST_MAPPINGS: 2.8787s 2.8781s 2.8785s 2.8742s 2.8759s
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>>
>
>> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 40
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>> (40 vcpus, 20G memory, block mappings(granule 1G))
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>> 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
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>>
>
>> Before patch: KVM_ADJUST_MAPPINGS: 103.931s 103.936s 103.927s 103.942s 103.927s
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>> After patch: KVM_ADJUST_MAPPINGS: 2.9621s 2.9648s 2.9474s 2.9587s 2.9603s
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>>
>
>> (2) performance change of patch 2, 3(based on patch 1)
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>> cmdline: ./kvm_page_table_test -m 4 -t 2 -g 1G -s 20G -v 1
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>> (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 -------
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>> arch/arm64/kvm/hyp/pgtable.c | 82 +++++++++++++++++++++-----------
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>> arch/arm64/kvm/mmu.c | 39 ++++++---------
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>> 3 files changed, 69 insertions(+), 68 deletions(-)
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>>
>
> .