From: Marc Zyngier <maz@kernel.org>
To: Reiji Watanabe <reijiw@google.com>
Cc: Oliver Upton <oupton@google.com>,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Andrew Jones <drjones@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Will Deacon <will@kernel.org>, Peter Shier <pshier@google.com>,
Ricardo Koller <ricarkol@google.com>,
Jing Zhang <jingzhangos@google.com>,
Raghavendra Rao Anata <rananta@google.com>
Subject: Re: [PATCH 2/2] KVM: arm64: selftests: Introduce get_set_regs_perf test
Date: Sat, 19 Feb 2022 09:42:19 +0000 [thread overview]
Message-ID: <3878ff49741733d6dd76aae57b594cb2@kernel.org> (raw)
In-Reply-To: <CAAeT=FxbbBq0sxUZAOSJW_wM+6M=xQe-p+=aeqpg=-y9VbpnnA@mail.gmail.com>
Hi Reiji,
On 2022-02-19 04:50, Reiji Watanabe wrote:
> Hi Marc,
>
> On Thu, Feb 17, 2022 at 1:12 AM Marc Zyngier <maz@kernel.org> wrote:
>>
>> On Thu, 17 Feb 2022 04:52:10 +0000,
>> Oliver Upton <oupton@google.com> wrote:
>>
>> > Would it make sense to test some opt-in capabilities that expose
>> > additional registers (PMU, SVE, etc.)?
>>
>> I think this is important. System registers are usually saved/restored
>
> Yes, I will fix the test to include registers for opt-in features
> when supported.
>
>> in groups, and due to the way we walk the sysreg array, timings are
>> unlikely to be uniform. Getting a grip on that could help restructure
>> the walking if required (either per-group arrays, or maybe a tree
>> structure).
>
> The biggest system register table that I know is sys_reg_descs[],
> and KVM_SET_ONE_REG/KVM_GET_ONE_REG/emulation code already uses
> binary search to find the target entry. So, the search itself
> isn't that bad. The difference between the min and the max
> latency of KVM_GET_ONE_REG for the registers is always around
> 200nsec on Ampere Altra machine as far as I checked.
Even if it is OK so far, it is bound to get worse over time, as
the architecture keeps adding all sort of things that we'll
eventually have to save/restore.
I see this test as a way to monitor this trend and work out when
we need to invest in something better.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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next prev parent reply other threads:[~2022-02-19 9:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-17 3:49 [PATCH 1/2] KVM: selftests: kvm_vm_elf_load() and elfhdr_get() should close fd Reiji Watanabe
2022-02-17 3:49 ` [PATCH 2/2] KVM: arm64: selftests: Introduce get_set_regs_perf test Reiji Watanabe
2022-02-17 4:52 ` Oliver Upton
2022-02-17 9:11 ` Marc Zyngier
2022-02-19 4:50 ` Reiji Watanabe
2022-02-19 9:42 ` Marc Zyngier [this message]
2022-02-19 3:53 ` Reiji Watanabe
2022-02-17 3:55 ` [PATCH 1/2] KVM: selftests: kvm_vm_elf_load() and elfhdr_get() should close fd Oliver Upton
2022-06-16 14:07 ` Andrew Jones
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