linux-kernel - Re: [PATCH RFC 1/1] perf stat: do not fatal if the leader is errored

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Date:   Thu, 22 Sep 2022 16:07:45 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, joe.jin@...cle.com,
        linux-perf-users@...r.kernel.org, kvm list <kvm@...r.kernel.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [PATCH RFC 1/1] perf stat: do not fatal if the leader is errored

On 22/9/2022 3:10 pm, Dongli Zhang wrote:
> There are three options to fix the issue.
> 
> 1. Do not expose /sys/bus/event_source/devices/cpu/events/slots to
> userspace so that pmu_have_event(pmu->name, "slots") returns false.

IMO, the guest PMU driver should be fixed
since it misrepresents emulated hardware capabilities in terms of slots.

> 
> 2. Run cpuid at perf userspace and avoid using 'slots' if it is not
> supported in cpuid.
> 
> 3. Do not fatal perf if the leader is failed. Do not create events for an
> evsel if its leader is already failed.

We may also need this since it's easier and more agile to update the perf tool
than the kernel code or KVM emulated capabilities.

> 
> This RFC patch is with the 3rd option. Would you mind suggesting which
> option is better?