From: Peter Zijlstra <peterz@infradead.org>
To: Joel Fernandes <joelaf@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
kernel-team@android.com, Ingo Molnar <mingo@redhat.com>,
Byungchul Park <byungchul.park@lge.com>,
Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 2/2] tracing: Add support for critical section events
Date: Mon, 4 Sep 2017 21:44:26 +0200 [thread overview]
Message-ID: <20170904194426.GD17526@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJWu+opjZaN4d2-+0jD3QwO+jEXx16WdY0Y_CrP4xihyoemgPQ@mail.gmail.com>
On Mon, Sep 04, 2017 at 12:04:44PM -0700, Joel Fernandes wrote:
> Hi Peter,
>
> On Mon, Sep 4, 2017 at 12:56 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Sun, Sep 03, 2017 at 01:50:51AM -0700, Joel Fernandes wrote:
> >> Critical section trace events can be used for tracing the start and
> >> end of a critical section which can be used by a trace viewer like
> >> systrace to graphically view the start and end of a critical section and
> >> correlate them with latencies and scheduling issues.
> >>
> >> Reason for starting critical section:
> >> Either preemption or interrupts were turned off.
> >> Reason for ending critical section:
> >> Both preemption and interrupts are now turned back on.
> >
> > Please don't use the name critical section for this.
>
> I can change the name to something else, but at the moment I can't
> think of anything better. Could you suggest a better name? Also btw,
> 'critical timings' is the terminology used within the irqsoff tracer
> so this is in line with that.
So 'critical section' is what some mis-guided people call the locked
region of a lock :-) Using it for something else is prone to cause more
confusion...
I would simply call them what they are: irq_disable,irq_enable
preempt_disable,preempt_enable.
> > Also IRQ and preempt already have a gazillion trace hooks, why do we need more?
>
> The goal of the patch is not to add more hooks, but to make it
> possible for userspace to use the trace-events mechanism to see these
> events, so that these events can be seen along with other trace events
> when using event tracing, using a convenient trace event interface
> which can be enabled by userspace.
But only when you're already building a debug kernel and we already have
these irq/preempt trace things in, right?
> This makes it possible to visually
> see these events as a timeline along with other kernel and userspace
> events. See more description in my coverletter [1] and a screenshot of
> how this is used [2] by the systrace trace viewer. These patches make
> it possible for this.
Yeah, for some reason these graphics things don't work for me... And
regular traces already have the irq-off and preempt-depth column, which
typically is enough. But I suppose I can see the value of allowing
explicit events for them.
> Also, this work is along the same lines of what we discussed in a
> recent conference about adding irqsoff and preemptoff as real trace
> events, and then using synthetic events (which can combine start and
> end event into a single event) to redo the irqsoff tracer, so in that
> sense it is in the right direction. Synthetic events is some time away
> though from being merged AFAIK.
I have no memories of that, but that sounds OK :-)
next prev parent reply other threads:[~2017-09-04 19:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-03 8:50 [PATCH 0/2] tracing: Add critical section event support Joel Fernandes
2017-09-03 8:50 ` [PATCH 1/2] tracing: irqsoff: Move code under tracer config options Joel Fernandes
2017-09-03 8:50 ` [PATCH 2/2] tracing: Add support for critical section events Joel Fernandes
2017-09-04 7:56 ` Peter Zijlstra
2017-09-04 19:04 ` Joel Fernandes
2017-09-04 19:44 ` Peter Zijlstra [this message]
2017-09-04 23:34 ` Steven Rostedt
2017-09-05 0:54 ` Joel Fernandes
2017-09-05 3:26 ` Joel Fernandes
2017-09-05 6:52 ` Peter Zijlstra
2017-09-05 16:35 ` Joel Fernandes
2017-09-06 8:40 ` Peter Zijlstra
2017-09-07 0:22 ` Joel Fernandes
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