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Subject: Re: [PATCH] KVM: x86: Adjust counter sample period after a wrmsr
To:     Eric Hankland <ehankland@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Peter Shier <pshier@google.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
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 <9adcb973-7b60-71dd-636d-1e451e664c55@redhat.com>
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 <CAOyeoRX8kXD4nHGCLk=pV2EHS4t9wykV5tYDfgKkTLBcN5=GGw@mail.gmail.com>
From:   Like Xu <like.xu@linux.intel.com>
Organization: Intel OTC
Message-ID: <8b48666a-c6a8-6dce-d784-424f5c447576@linux.intel.com>
Date:   Wed, 26 Feb 2020 11:04:02 +0800
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On 2020/2/25 8:08, Eric Hankland wrote:
> Hi Like -
> 
> Thanks for the feedback - is your recommendation to do the read and
> period change at the same time and only take the lock once or is there
> another way around this while still handling writes correctly?

For non-running counters(the most common situation), we have too many
chances to reflect their new periods. In this case, calling
perf_event_period() in the trap of counter msr is redundant and burdensome.

A better way is to check if this counter is running via
pmc_speculative_in_use (), and if so,
just trigger kvm_make_request(KVM_REQ_PMU, pmc->vcpu).

Thanks,
Like Xu

> 
> Eric
>