linux-kernel - Re: [Patch v5 16/19] perf/x86: Activate back-to-back NMI detection for arch-PEBS induced NMIs

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Message-ID: <20251208085020.GA3707891@noisy.programming.kicks-ass.net>
Date: Mon, 8 Dec 2025 09:50:20 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>,
	Mark Rutland <mark.rutland@....com>, broonie@...nel.org,
	Ravi Bangoria <ravi.bangoria@....com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, Zide Chen <zide.chen@...el.com>,
	Falcon Thomas <thomas.falcon@...el.com>,
	Dapeng Mi <dapeng1.mi@...el.com>, Xudong Hao <xudong.hao@...el.com>
Subject: Re: [Patch v5 16/19] perf/x86: Activate back-to-back NMI detection
 for arch-PEBS induced NMIs

On Mon, Dec 08, 2025 at 02:46:44PM +0800, Mi, Dapeng wrote:

> This change only take effects for arch-PEBS. For the legacy PEBS, the
> "handled" would still be added 1 unconditionally even the *_drain_pebs()
> helpers always return 0.
> 
>     /*
>      * PEBS overflow sets bit 62 in the global status register
>      */
>     if (__test_and_clear_bit(GLOBAL_STATUS_BUFFER_OVF_BIT, (unsigned long
> *)&status)) {
>         u64 pebs_enabled = cpuc->pebs_enabled;
> 
>         handled++;
>         x86_pmu_handle_guest_pebs(regs, &data);
>         static_call(x86_pmu_drain_pebs)(regs, &data);
> 

Oh gawd. Please don't do that. If you change the calling convention of
that function, please have it be used consistently.