linux-kernel - Re: [Patch v3 3/7] perf/x86: Check if cpuc->events[*] pointer exists before accessing it

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Message-ID: <fab2a035-5ab3-4e24-bd3e-760a4b9be5e8@linux.intel.com>
Date: Wed, 20 Aug 2025 13:54:17 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Andi Kleen <ak@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Eranian Stephane
 <eranian@...gle.com>, linux-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org, Dapeng Mi <dapeng1.mi@...el.com>,
 kernel test robot <oliver.sang@...el.com>
Subject: Re: [Patch v3 3/7] perf/x86: Check if cpuc->events[*] pointer exists
 before accessing it


On 8/20/2025 1:44 PM, Andi Kleen wrote:
>> Andi, I didn't fully get the exact meaning about the "log" here. When
>> throttle is triggered, perf_event_throttle() has already called
>> perf_log_throttle() to log the throttle event although only for the group
>> leader. Is it enough?
> Throttle normally doesn't involve data loss, just less samples. But this
> is data loss, so it's an overflow.

IIUC, there should be no data loss, the unprocessed PEBS records of these
throttled events would be still processed eventually by calling
intel_pmu_drain_pebs_buffer() when stopping the event.


>
> -Andi
>