linux-kernel - Re: [PATCH v5 bpf-next 1/3] perf: enable branch record for software events

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Message-ID: <YTHcXDhYDFsw9GQX@hirez.programming.kicks-ass.net>
Date:   Fri, 3 Sep 2021 10:27:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        mingo@...hat.com, kjain@...ux.ibm.com, kernel-team@...com
Subject: Re: [PATCH v5 bpf-next 1/3] perf: enable branch record for software
 events

On Thu, Sep 02, 2021 at 09:57:04AM -0700, Song Liu wrote:

> +static int
> +intel_pmu_snapshot_branch_stack(struct perf_branch_entry *entries, unsigned int cnt)
> +{
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +
> +	intel_pmu_disable_all();
> +	intel_pmu_lbr_read();
> +	cnt = min_t(unsigned int, cnt, x86_pmu.lbr_nr);
> +
> +	memcpy(entries, cpuc->lbr_entries, sizeof(struct perf_branch_entry) * cnt);
> +	intel_pmu_enable_all(0);
> +	return cnt;
> +}

Given this disables the PMI from 'random' contexts, should we not add
IRQ disabling around this to avoid really bad behaviour?