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

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Message-ID: <aedbcbb5-f0b4-4bf6-bc33-c8c3bf3f20bc@linux.intel.com>
Date: Wed, 20 Aug 2025 13:33:28 +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 11:41 AM, Andi Kleen wrote:
>>  		event = cpuc->events[bit];
>> +		/*
>> +		 * perf_event_overflow() called by below __intel_pmu_pebs_last_event()
>> +		 * could trigger interrupt throttle and clear all event pointers of the
>> +		 * group in cpuc->events[] to NULL. So need to re-check if cpuc->events[*]
>> +		 * is NULL, if so it indicates the event has been throttled (stopped) and
>> +		 * the corresponding last PEBS records have been processed in stopping
>> +		 * event, don't need to process it again.
>> +		 */
>> +		if (!event)
>> +			continue;
> Then we silently ignore the overflow. Would be better to log at least an overflow
> packet or something like that.

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?


>
> -Andi
>