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From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 3/3] ftrace: function tracer with irqs disabled
Date: Tue, 4 Nov 2008 09:07:47 +0100	[thread overview]
Message-ID: <20081104080747.GA27075@elte.hu> (raw)
In-Reply-To: <20081104042203.499871423@goodmis.org>


* Steven Rostedt <rostedt@goodmis.org> wrote:

> Running hackbench 3 times with the irqs disabled and 3 times with 
> the preempt disabled function tracer yielded:
> 
> tracing type       times            entries recorded
> ------------      --------          ----------------
> irq disabled      43.393            166433066
>                   43.282            166172618
>                   43.298            166256704
> 
> preempt disabled  38.969            159871710
>                   38.943            159972935
>                   39.325            161056510

your numbers might be correct, but i found that hackbench is not 
reliable boot-to-boot - it can easily produce 10% systematic noise or 
more. (perhaps depending on how the various socket data structures 
happen to be allocated)

the really conclusive way to test this would be to add a hack that 
either does preempt disable or irqs disable, depending on a runtime 
flag - and then observe how hackbench performance reacts to the value 
of that flag.

note that preempt-disable will also produce less trace entries, 
especially in very irq-rich workloads. Hence it will be "faster".

	Ingo

  reply	other threads:[~2008-11-04  8:08 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-04  4:15 [PATCH 0/3] ftrace: code consolidation Steven Rostedt
2008-11-04  4:15 ` [PATCH 1/3] ftrace: ftrace_preempt_disable Steven Rostedt
2008-11-04  9:10   ` Ingo Molnar
2008-11-04 21:48     ` [PATCH] ftrace: ftrace_preempt_disable comment fix Steven Rostedt
2008-11-04 21:52       ` [PATCH v2] " Steven Rostedt
2008-11-04 22:05         ` [PATCH v3] " Steven Rostedt
2008-11-04  4:15 ` [PATCH 2/3] ftrace: insert in the ftrace_preempt_disable functions Steven Rostedt
2008-11-04  4:15 ` [PATCH 3/3] ftrace: function tracer with irqs disabled Steven Rostedt
2008-11-04  8:07   ` Ingo Molnar [this message]
2008-11-04  8:17     ` Zhang, Yanmin
2008-11-04  9:04     ` Ingo Molnar
2008-11-04 14:44       ` Steven Rostedt
2008-11-04 16:43         ` Ingo Molnar

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