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From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org,
	irogers@google.com, linux-kernel@vger.kernel.org,
	linux-perf-users@vger.kernel.org, ak@linux.intel.com,
	eranian@google.com, dapeng1.mi@linux.intel.com
Subject: Re: [PATCH V6 3/3] perf/x86/intel: Support PEBS counters snapshotting
Date: Wed, 18 Dec 2024 11:55:53 -0500	[thread overview]
Message-ID: <3d63f8b2-c028-4cae-ad72-76378425c73a@linux.intel.com> (raw)
In-Reply-To: <20241218163249.GI2354@noisy.programming.kicks-ass.net>



On 2024-12-18 11:32 a.m., Peter Zijlstra wrote:
> On Wed, Dec 18, 2024 at 07:16:43AM -0800, kan.liang@linux.intel.com wrote:
> 
>> To prevent the case that a PEBS record value might be in the past
>> relative to what is already in the event, perf always stops the PMU and
>> drains the PEBS buffer before updating the corresponding event->count.
> 
> Like I wrote here:
> 
>   https://lkml.kernel.org/r/20241218082404.GI11133@noisy.programming.kicks-ass.net
> 
> I don't think this is sufficient.


I replied with an explanation this morning in the old V5 thread. I'm not
sure if you got a chance to look at it.
https://lore.kernel.org/all/5a4ab06e-8628-4e1d-addb-2af920deffad@linux.intel.com/

There will be a drain_pebs() right before handling A-overflow-PMI.

  B-assist			A=1
  C				A=2
  B-assist			A=3
  		<- drain_pebs()
  A-overflow-PMI		A=4
  C-assist-PMI (DS buffer)	A=5

So the A-overflow-PMI will
   - Process the DS. adjust A->count to 3
   - adjust A->count to 4

Is it sufficient?
If not, could you please share more details?

Thanks,
Kan



  reply	other threads:[~2024-12-18 16:55 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-12-18 15:16 [PATCH V6 1/3] perf/x86/intel/ds: Add PEBS format 6 kan.liang
2024-12-18 15:16 ` [PATCH V6 2/3] perf: Extend perf_output_read kan.liang
2024-12-19 22:21   ` Peter Zijlstra
2024-12-20  0:42     ` Liang, Kan
2024-12-18 15:16 ` [PATCH V6 3/3] perf/x86/intel: Support PEBS counters snapshotting kan.liang
2024-12-18 16:32   ` Peter Zijlstra
2024-12-18 16:55     ` Liang, Kan [this message]
2024-12-18 17:01       ` Peter Zijlstra
2024-12-20 14:22   ` Peter Zijlstra
2025-01-03 16:15     ` Liang, Kan

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