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Date: Fri, 13 Feb 2009 21:03:08 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>, Thomas Gleixner <tglx@tglx.de>,
       LKML <linux-kernel@vger.kernel.org>,
       rt-users <linux-rt-users@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Peter Zijlstra <peterz@infradead.org>, Carsten Emde <ce@ceag.ch>,
       Clark Williams <williams@redhat.com>
Subject: Re: [patch] rt: sysprof hrtimer fix
Message-ID: <20090213200305.GA5833@nowhere>
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On Fri, Feb 13, 2009 at 01:49:28PM +0100, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@gmail.com> wrote:
> 
> > So, just a thing.
> > -rt make the hrtimer's timers running on softirq context because the hrtimer_interrupt
> > doesn't run as a threaded interrupt, and then it is not preemptible right?
> > 
> > In that case, sysprof will continue to run in hardirq context, as before, and
> > it will considerably increase the latency. And that matters here.
> > So I think it is important to put it on the reminder:
> 
> hm, not sure. Do you know it numerically how much worst-case overhead it
> induces?
> 
> 	Ingo

Not at all.
But when I find some time, I will compare some rt average tests with and without sysprof.