From: Ricardo Koller <ricarkol@google.com>
To: Jing Zhang <jingzhangos@google.com>
Cc: KVM <kvm@vger.kernel.org>, KVMARM <kvmarm@lists.cs.columbia.edu>,
Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
David Matlack <dmatlack@google.com>,
Oliver Upton <oupton@google.com>,
Reiji Watanabe <reijiw@google.com>
Subject: Re: [RFC PATCH 0/3] ARM64: Guest performance improvement during dirty
Date: Wed, 12 Jan 2022 18:49:59 -0800 [thread overview]
Message-ID: <Yd+TV4Bkhzpnpx8N@google.com> (raw)
In-Reply-To: <20220110210441.2074798-1-jingzhangos@google.com>
Hi Jing,
On Mon, Jan 10, 2022 at 09:04:38PM +0000, Jing Zhang wrote:
> This patch is to reduce the performance degradation of guest workload during
> dirty logging on ARM64. A fast path is added to handle permission relaxation
> during dirty logging. The MMU lock is replaced with rwlock, by which all
> permision relaxations on leaf pte can be performed under the read lock. This
> greatly reduces the MMU lock contention during dirty logging. With this
> solution, the source guest workload performance degradation can be improved
> by more than 60%.
>
> Problem:
> * A Google internal live migration test shows that the source guest workload
> performance has >99% degradation for about 105 seconds, >50% degradation
> for about 112 seconds, >10% degradation for about 112 seconds on ARM64.
> This shows that most of the time, the guest workload degradtion is above
> 99%, which obviously needs some improvement compared to the test result
> on x86 (>99% for 6s, >50% for 9s, >10% for 27s).
> * Tested H/W: Ampere Altra 3GHz, #CPU: 64, #Mem: 256GB
> * VM spec: #vCPU: 48, #Mem/vCPU: 4GB
>
> Analysis:
> * We enabled CONFIG_LOCK_STAT in kernel and used dirty_log_perf_test to get
> the number of contentions of MMU lock and the "dirty memory time" on
> various VM spec.
> By using test command
> ./dirty_log_perf_test -b 2G -m 2 -i 2 -s anonymous_hugetlb_2mb -v [#vCPU]
> Below are the results:
> +-------+------------------------+-----------------------+
> | #vCPU | dirty memory time (ms) | number of contentions |
> +-------+------------------------+-----------------------+
> | 1 | 926 | 0 |
> +-------+------------------------+-----------------------+
> | 2 | 1189 | 4732558 |
> +-------+------------------------+-----------------------+
> | 4 | 2503 | 11527185 |
> +-------+------------------------+-----------------------+
> | 8 | 5069 | 24881677 |
> +-------+------------------------+-----------------------+
> | 16 | 10340 | 50347956 |
> +-------+------------------------+-----------------------+
> | 32 | 20351 | 100605720 |
> +-------+------------------------+-----------------------+
> | 64 | 40994 | 201442478 |
> +-------+------------------------+-----------------------+
>
> * From the test results above, the "dirty memory time" and the number of
> MMU lock contention scale with the number of vCPUs. That means all the
> dirty memory operations from all vCPU threads have been serialized by
> the MMU lock. Further analysis also shows that the permission relaxation
> during dirty logging is where vCPU threads get serialized.
>
> Solution:
> * On ARM64, there is no mechanism as PML (Page Modification Logging) and
> the dirty-bit solution for dirty logging is much complicated compared to
> the write-protection solution. The straight way to reduce the guest
> performance degradation is to enhance the concurrency for the permission
> fault path during dirty logging.
> * In this patch, we only put leaf PTE permission relaxation for dirty
> logging under read lock, all others would go under write lock.
> Below are the results based on the solution:
> +-------+------------------------+
> | #vCPU | dirty memory time (ms) |
> +-------+------------------------+
> | 1 | 803 |
> +-------+------------------------+
> | 2 | 843 |
> +-------+------------------------+
> | 4 | 942 |
> +-------+------------------------+
> | 8 | 1458 |
> +-------+------------------------+
> | 16 | 2853 |
> +-------+------------------------+
> | 32 | 5886 |
> +-------+------------------------+
> | 64 | 12190 |
> +-------+------------------------+
Just curious, do yo know why is time still doubling (roughly) with the
number of cpus? maybe you performed another experiment or have some
guess(es).
Thanks,
Ricardo
> All "dirty memory time" have been reduced by more than 60% when the
> number of vCPU grows.
>
> ---
>
> Jing Zhang (3):
> KVM: arm64: Use read/write spin lock for MMU protection
> KVM: arm64: Add fast path to handle permission relaxation during dirty
> logging
> KVM: selftests: Add vgic initialization for dirty log perf test for
> ARM
>
> arch/arm64/include/asm/kvm_host.h | 2 +
> arch/arm64/kvm/mmu.c | 86 +++++++++++++++----
> .../selftests/kvm/dirty_log_perf_test.c | 10 +++
> 3 files changed, 80 insertions(+), 18 deletions(-)
>
>
> base-commit: fea31d1690945e6dd6c3e89ec5591490857bc3d4
> --
> 2.34.1.575.g55b058a8bb-goog
>
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
next prev parent reply other threads:[~2022-01-13 2:50 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-10 21:04 [RFC PATCH 0/3] ARM64: Guest performance improvement during dirty Jing Zhang
2022-01-10 21:04 ` [RFC PATCH 1/3] KVM: arm64: Use read/write spin lock for MMU protection Jing Zhang
2022-01-11 10:23 ` Marc Zyngier
2022-01-11 22:12 ` Jing Zhang
2022-01-10 21:04 ` [RFC PATCH 2/3] KVM: arm64: Add fast path to handle permission relaxation during dirty logging Jing Zhang
2022-01-11 10:22 ` Marc Zyngier
2022-01-11 10:50 ` Marc Zyngier
2022-01-11 22:12 ` Jing Zhang
2022-01-10 21:04 ` [RFC PATCH 3/3] KVM: selftests: Add vgic initialization for dirty log perf test for ARM Jing Zhang
2022-01-11 9:55 ` Andrew Jones
2022-01-11 22:12 ` Jing Zhang
2022-01-11 10:30 ` Marc Zyngier
2022-01-11 22:16 ` Jing Zhang
2022-01-12 11:37 ` Marc Zyngier
2022-01-12 17:40 ` Jing Zhang
2022-01-11 11:54 ` [RFC PATCH 0/3] ARM64: Guest performance improvement during dirty Marc Zyngier
2022-01-11 22:12 ` Jing Zhang
2022-01-13 2:49 ` Ricardo Koller [this message]
2022-01-13 3:50 ` Jing Zhang
2022-01-13 6:12 ` Ricardo Koller
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