Subject: Re: [PATCH] clean up FIXME in do_timer_interrupt
From: Lee Revell <rlrevell@joe-job.com>
To: george@mvista.com
Cc: Andrew Morton <akpm@osdl.org>, mingo@elte.hu, linux-kernel@vger.kernel.org
In-Reply-To: <4228CBFB.3000602@mvista.com>
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Date: Tue, 08 Mar 2005 15:27:24 -0500
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On Fri, 2005-03-04 at 12:58 -0800, George Anzinger wrote:
> Lee Revell wrote:
> > On Fri, 2005-03-04 at 02:28 -0800, George Anzinger wrote:
> > The thing that brought this code to my attention is that with PREEMPT_RT
> > this happens to be the longest non-preemptible code path in the kernel.
> > On my 1.3 Ghz machine set_rtc_mmss takes about 50 usecs, combined with
> > the rest of timer irq we end up disabling preemption for about 90 usecs.
> > Unfortunately I don't have the trace anymore.
> > 
> > Anyway the upshot is if we hung this off a timer it looks like we would
> > improve the worst case latency with PREEMPT_RT by almost 50%.  Unless
> > there is some reason it has to be done synchronously of course.
> 
> Well, it does have to be done at the right WRT the second, but I suspect we can 
> hit that as well with a timer as it is hit now.  Also, if we are _really_ off 
> the mark, this can be defered till the next second.
> 

Do you have a patch?

Andrew merged my trivial patch to clean up the logic, but a real fix
would be better.

Lee

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