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From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>,
	linux-kernel@vger.kernel.org, williams@redhat.com,
	daniel@bristot.me, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Yangtao Li <tiny.windzz@gmail.com>,
	Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>
Subject: Re: [RFC 2/3] preempt_tracer: Disable IRQ while starting/stopping due to a preempt_counter change
Date: Wed, 29 May 2019 15:29:26 +0200	[thread overview]
Message-ID: <20190529132926.GV2650@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190529131957.GV2623@hirez.programming.kicks-ass.net>

On Wed, May 29, 2019 at 03:19:57PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 08:39:30AM -0400, Steven Rostedt wrote:
> > I believe I see what Daniel is talking about, but I hate the proposed
> > solution ;-)
> > 
> > First, if you care about real times that the CPU can't preempt
> > (preempt_count != 0 or interrupts disabled), then you want the
> > preempt_irqsoff tracer. The preempt_tracer is more academic where it
> > just shows you when we disable preemption via the counter. But even
> > with the preempt_irqsoff tracer you may not get the full length of time
> > due to the above explained race.
> 
> IOW, that tracer gives a completely 'make believe' number? What's the
> point? Just delete the pure preempt tracer.

Alternatively, fix the preempt tracer by having it completely disregard
IRQs.

  reply	other threads:[~2019-05-29 13:30 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-28 15:16 [RFC 0/3] preempt_tracer: Fix preempt_disable tracepoint Daniel Bristot de Oliveira
2019-05-28 15:16 ` [RFC 1/3] softirq: Use preempt_latency_stop/start to trace preemption Daniel Bristot de Oliveira
2019-05-29  8:29   ` Peter Zijlstra
2019-05-29  9:30   ` Joel Fernandes
2019-05-29 12:22     ` Steven Rostedt
2019-06-04 10:39       ` Daniel Bristot de Oliveira
2019-06-04 12:01         ` Steven Rostedt
2019-05-28 15:16 ` [RFC 2/3] preempt_tracer: Disable IRQ while starting/stopping due to a preempt_counter change Daniel Bristot de Oliveira
2019-05-29  8:33   ` Peter Zijlstra
2019-05-29  9:40     ` Daniel Bristot de Oliveira
2019-05-29 10:20       ` Peter Zijlstra
2019-05-29 12:39         ` Steven Rostedt
2019-05-29 13:19           ` Peter Zijlstra
2019-05-29 13:29             ` Peter Zijlstra [this message]
2019-05-29 13:42             ` Steven Rostedt
2019-05-29 13:49               ` Peter Zijlstra
2019-05-29 13:58                 ` Steven Rostedt
2019-05-29 13:51         ` Daniel Bristot de Oliveira
2019-05-29 18:21           ` Peter Zijlstra
2019-06-04 10:20             ` Daniel Bristot de Oliveira
2019-05-31  7:47       ` Joel Fernandes
2019-06-04 10:12         ` Daniel Bristot de Oliveira
2019-06-04 15:01           ` Steven Rostedt
2019-06-05 15:16             ` Joel Fernandes
2019-05-28 15:16 ` [RFC 3/3] preempt_tracer: Use a percpu variable to control traceble calls Daniel Bristot de Oliveira
2019-05-29  8:41   ` Peter Zijlstra
2019-05-29  9:48     ` Daniel Bristot de Oliveira

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