From: Andi Kleen <ak@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Jiri Olsa <jolsa@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Eranian Stephane <eranian@google.com>,
Mark Rutland <mark.rutland@arm.com>,
broonie@kernel.org, Ravi Bangoria <ravi.bangoria@amd.com>,
linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
Zide Chen <zide.chen@intel.com>,
Falcon Thomas <thomas.falcon@intel.com>,
Dapeng Mi <dapeng1.mi@intel.com>,
Xudong Hao <xudong.hao@intel.com>
Subject: Re: [Patch v5 16/19] perf/x86: Activate back-to-back NMI detection for arch-PEBS induced NMIs
Date: Sun, 7 Dec 2025 12:44:26 -0800 [thread overview]
Message-ID: <aTXnKl2oCmrp11eq@tassilo> (raw)
In-Reply-To: <20251205123940.GY2528459@noisy.programming.kicks-ass.net>
On Fri, Dec 05, 2025 at 01:39:40PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 03, 2025 at 02:54:57PM +0800, Dapeng Mi wrote:
> > When two or more identical PEBS events with the same sampling period are
> > programmed on a mix of PDIST and non-PDIST counters, multiple
> > back-to-back NMIs can be triggered.
>
> This is a hardware defect -- albeit a fairly common one.
Actually I disagree on that. PEBS is essentially a shared memory
protocol between two asynchronous agents. To prevent this you would need a
locking protocol somehow for the memory, otherwise the sender (PEBS) has
no way to know that the PMI handler is finished reading the memory
buffers.
So it cannot know that the second event was already parsed, and
has to send the second PMI just in case.
It didn't happen with the legacy PEBS because it always
collapsed multiple counters into one, but that was really a race
too.
-Andi
next prev parent reply other threads:[~2025-12-07 20:44 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-03 6:54 [Patch v5 00/19] Support SIMD/eGPRs/SSP registers sampling for perf Dapeng Mi
2025-12-03 6:54 ` [Patch v5 01/19] perf: Eliminate duplicate arch-specific functions definations Dapeng Mi
2025-12-03 6:54 ` [Patch v5 02/19] perf/x86: Use x86_perf_regs in the x86 nmi handler Dapeng Mi
2025-12-03 6:54 ` [Patch v5 03/19] perf/x86: Introduce x86-specific x86_pmu_setup_regs_data() Dapeng Mi
2025-12-03 6:54 ` [Patch v5 04/19] x86/fpu/xstate: Add xsaves_nmi() helper Dapeng Mi
2025-12-03 6:54 ` [Patch v5 05/19] perf: Move and rename has_extended_regs() for ARCH-specific use Dapeng Mi
2025-12-03 6:54 ` [Patch v5 06/19] perf/x86: Add support for XMM registers in non-PEBS and REGS_USER Dapeng Mi
2025-12-04 15:17 ` Peter Zijlstra
2025-12-04 15:47 ` Peter Zijlstra
2025-12-05 6:37 ` Mi, Dapeng
2025-12-04 18:59 ` Dave Hansen
2025-12-05 8:42 ` Peter Zijlstra
2025-12-03 6:54 ` [Patch v5 07/19] perf: Add sampling support for SIMD registers Dapeng Mi
2025-12-05 11:07 ` Peter Zijlstra
2025-12-08 5:24 ` Mi, Dapeng
2025-12-05 11:40 ` Peter Zijlstra
2025-12-08 6:00 ` Mi, Dapeng
2025-12-03 6:54 ` [Patch v5 08/19] perf/x86: Enable XMM sampling using sample_simd_vec_reg_* fields Dapeng Mi
2025-12-05 11:25 ` Peter Zijlstra
2025-12-08 6:10 ` Mi, Dapeng
2025-12-03 6:54 ` [Patch v5 09/19] perf/x86: Enable YMM " Dapeng Mi
2025-12-03 6:54 ` [Patch v5 10/19] perf/x86: Enable ZMM " Dapeng Mi
2025-12-03 6:54 ` [Patch v5 11/19] perf/x86: Enable OPMASK sampling using sample_simd_pred_reg_* fields Dapeng Mi
2025-12-03 6:54 ` [Patch v5 12/19] perf/x86: Enable eGPRs sampling using sample_regs_* fields Dapeng Mi
2025-12-05 12:16 ` Peter Zijlstra
2025-12-08 6:11 ` Mi, Dapeng
2025-12-03 6:54 ` [Patch v5 13/19] perf/x86: Enable SSP " Dapeng Mi
2025-12-05 12:20 ` Peter Zijlstra
2025-12-08 6:21 ` Mi, Dapeng
2025-12-03 6:54 ` [Patch v5 14/19] perf/x86/intel: Enable PERF_PMU_CAP_SIMD_REGS capability Dapeng Mi
2025-12-03 6:54 ` [Patch v5 15/19] perf/x86/intel: Enable arch-PEBS based SIMD/eGPRs/SSP sampling Dapeng Mi
2025-12-03 6:54 ` [Patch v5 16/19] perf/x86: Activate back-to-back NMI detection for arch-PEBS induced NMIs Dapeng Mi
2025-12-05 12:39 ` Peter Zijlstra
2025-12-07 20:44 ` Andi Kleen [this message]
2025-12-08 6:46 ` Mi, Dapeng
2025-12-08 8:50 ` Peter Zijlstra
2025-12-08 8:53 ` Mi, Dapeng
2025-12-03 6:54 ` [Patch v5 17/19] perf headers: Sync with the kernel headers Dapeng Mi
2025-12-03 23:43 ` Ian Rogers
2025-12-04 1:37 ` Mi, Dapeng
2025-12-04 7:28 ` Ian Rogers
2025-12-03 6:54 ` [Patch v5 18/19] perf parse-regs: Support new SIMD sampling format Dapeng Mi
2025-12-04 0:17 ` Ian Rogers
2025-12-04 2:58 ` Mi, Dapeng
2025-12-04 7:49 ` Ian Rogers
2025-12-04 9:20 ` Mi, Dapeng
2025-12-04 16:16 ` Ian Rogers
2025-12-05 4:00 ` Mi, Dapeng
2025-12-05 6:38 ` Ian Rogers
2025-12-05 8:10 ` Mi, Dapeng
2025-12-05 16:35 ` Ian Rogers
2025-12-08 4:20 ` Mi, Dapeng
2025-12-03 6:55 ` [Patch v5 19/19] perf regs: Enable dumping of SIMD registers Dapeng Mi
2025-12-04 0:24 ` [Patch v5 00/19] Support SIMD/eGPRs/SSP registers sampling for perf Ian Rogers
2025-12-04 3:28 ` Mi, Dapeng
2025-12-16 4:42 ` Ravi Bangoria
2025-12-16 6:59 ` Mi, Dapeng
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