Re: [PATCH 2/2] tracing: Add support for critical section events

From	Joel Fernandes <joelaf@google.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] tracing: Add support for critical section events
Date	2017-09-05 18:40 +0200
Message-ID	<ump3j-5bD-1@gated-at.bofh.it> (permalink)
References	(4 earlier) <um5xD-1a2-9@gated-at.bofh.it> <um98f-3rq-5@gated-at.bofh.it> <umanE-47H-9@gated-at.bofh.it> <umcIO-5Nm-7@gated-at.bofh.it> <umg02-7JL-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Sep 4, 2017 at 11:52 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Sep 04, 2017 at 08:26:13PM -0700, Joel Fernandes wrote:
>
>> Apologies, I meant (without the "off"):
>>
>> subsystem: atomic_section
>> events:
>>   irqs_disable
>>   irqs_enable
>>   preempt_disable
>>   preempt_enable
>>
>> and additionally (similar to what my patch does):
>>   preemptirq_enable
>>   preemptirq_disable
>>
>
> What do you need the last for?

The last 2 events above behave as 'disable' means either preempt or
irq got disabled, and 'enable' means *both* preempt and irq are
enabled (after either one of them was disabled).

This has the advantage of not generating events when we're already in
an atomic section when using these events, for example acquiring spin
locks in an interrupt handler might increase the preempt count and
generate 'preempt_disable' events, but not preemptirq_disable events.
This has the effect of reducing the spam in the traces when all we
care about is being in an atomic section or not. These events happen a
lot so to conserve space in the trace buffer, the user may want to
just enable the latter 2 events. Does that sound Ok to you?

thanks,

- Joel

Thread

[PATCH 2/2] tracing: Add support for critical section events Joel Fernandes <joelaf@google.com> - 2017-09-03 11:00 +0200
  Re: [PATCH 2/2] tracing: Add support for critical section events Peter Zijlstra <peterz@infradead.org> - 2017-09-04 10:00 +0200
    Re: [PATCH 2/2] tracing: Add support for critical section events Joel Fernandes <joelaf@google.com> - 2017-09-04 21:10 +0200
      Re: [PATCH 2/2] tracing: Add support for critical section events Peter Zijlstra <peterz@infradead.org> - 2017-09-04 21:50 +0200
        Re: [PATCH 2/2] tracing: Add support for critical section events Steven Rostedt <rostedt@goodmis.org> - 2017-09-05 01:40 +0200
          Re: [PATCH 2/2] tracing: Add support for critical section events Joel Fernandes <joelaf@google.com> - 2017-09-05 03:00 +0200
            Re: [PATCH 2/2] tracing: Add support for critical section events Joel Fernandes <joelaf@google.com> - 2017-09-05 05:30 +0200
              Re: [PATCH 2/2] tracing: Add support for critical section events Peter Zijlstra <peterz@infradead.org> - 2017-09-05 09:00 +0200
                Re: [PATCH 2/2] tracing: Add support for critical section events Joel Fernandes <joelaf@google.com> - 2017-09-05 18:40 +0200
                Re: [PATCH 2/2] tracing: Add support for critical section events Peter Zijlstra <peterz@infradead.org> - 2017-09-06 10:50 +0200
                Re: [PATCH 2/2] tracing: Add support for critical section events Joel Fernandes <joelaf@google.com> - 2017-09-07 02:30 +0200

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