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Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the kernel in the "skid" region

From "Jin, Yao" <yao.jin@linux.intel.com>
Newsgroups linux.kernel
Subject Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the kernel in the "skid" region
Date 2017-06-28 04:10 +0200
Message-ID <tXaAy-Ds-3@gated-at.bofh.it> (permalink)
References <tX9Eu-8wj-27@gated-at.bofh.it> <tX9Eu-8wj-25@gated-at.bofh.it>
Organization linux.* mail to news gateway

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Hi,

In theory, the PMI interrupts in skid region should be dropped, right?

For a userspace debugger, is it the only choice that relies on the 
*skid* PMI interrupt?

Thanks
Jin Yao

On 6/28/2017 9:01 AM, Kyle Huey wrote:
> Sent again with LKML CCd, sorry for the noise.
>
> - Kyle
>
> On Tue, Jun 27, 2017 at 5:38 PM, Kyle Huey <me@kylehuey.com> wrote:
>> cc1582c231ea introduced a regression in v4.12.0-rc5, and appears to be
>> a candidate for backporting to stable branches.
>>
>> rr, a userspace record and replay debugger[0], uses the PMU interrupt
>> to stop a program during replay to inject asynchronous events such as
>> signals.  We are counting retired conditional branches in userspace
>> only.  This changeset causes the kernel to drop interrupts on the
>> floor if, during the PMU interrupt's "skid" region, the CPU enters
>> kernel mode for whatever reason.  When replaying traces of complex
>> programs such as Firefox, we intermittently fail to deliver
>> asynchronous events on time, leading the replay to diverge from the
>> recorded state.
>>
>> It seems like this change should, at a bare minimum, be limited to
>> counters that actually perform sampling of register state when the
>> interrupt fires.  In our case, with the retired conditional branches
>> counter restricted to counting userspace events only, it makes no
>> difference that the PMU interrupt happened to be delivered in the
>> kernel.
>>
>> As this makes rr unusable on complex applications and cannot be
>> efficiently worked around, we would appreciate this being addressed
>> before 4.12 is finalized, and the regression not being introduced to
>> stable branches.
>>
>> Thanks,
>>
>> - Kyle
>>
>> [0] http://rr-project.org/

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Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Kyle Huey <me@kylehuey.com> - 2017-06-28 03:10 +0200
  Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region "Jin, Yao" <yao.jin@linux.intel.com> - 2017-06-28 04:10 +0200
    Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Kyle Huey <me@kylehuey.com> - 2017-06-28 07:00 +0200
      Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region "Jin, Yao" <yao.jin@linux.intel.com> - 2017-06-28 07:40 +0200
        Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Kyle Huey <me@kylehuey.com> - 2017-06-28 09:40 +0200
      Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Mark Rutland <mark.rutland@arm.com> - 2017-06-28 12:20 +0200
        [PATCH] perf/core: generate overflow signal when samples are dropped  (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region) Mark Rutland <mark.rutland@arm.com> - 2017-06-28 13:00 +0200
          Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Vince Weaver <vincent.weaver@maine.edu> - 2017-06-28 14:50 +0200
            Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Mark Rutland <mark.rutland@arm.com> - 2017-06-28 15:10 +0200
              Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Alexey Budankov <alexey.budankov@linux.intel.com> - 2017-06-29 10:20 +0200
                Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Alexey Budankov <alexey.budankov@linux.intel.com> - 2017-06-29 10:30 +0200
          Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Mark Rutland <mark.rutland@arm.com> - 2017-06-28 20:00 +0200
            Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Kyle Huey <me@kylehuey.com> - 2017-06-29 01:00 +0200
              Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) "Jin, Yao" <yao.jin@linux.intel.com> - 2017-06-29 02:30 +0200
              Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Kyle Huey <me@kylehuey.com> - 2017-06-30 19:50 +0200
            Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Ingo Molnar <mingo@kernel.org> - 2017-06-29 10:20 +0200
          Re: [PATCH] perf/core: generate overflow signal when samples are  dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we  entered the kernel in the "skid" region) Kyle Huey <me@kylehuey.com> - 2017-06-28 20:00 +0200
        Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region "Robert O'Callahan" <robert@ocallahan.org> - 2017-06-28 20:00 +0200
        Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Kyle Huey <me@kylehuey.com> - 2017-06-28 20:00 +0200
          Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Mark Rutland <mark.rutland@arm.com> - 2017-06-28 20:00 +0200
        Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Mark Rutland <mark.rutland@arm.com> - 2017-06-28 20:00 +0200
        Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the  kernel in the "skid" region Kyle Huey <me@kylehuey.com> - 2017-06-28 20:00 +0200

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