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From: John <shill@free.fr>
To: linux-kernel@vger.kernel.org
Cc: tglx@timesys.com, mingo@elte.hu, johnstul@us.ibm.com,
	akpm@osdl.org, shill@free.fr
Subject: Re: One-shot high-resolution POSIX timer periodically late
Date: Thu, 25 Jan 2007 13:03:37 +0100	[thread overview]
Message-ID: <45B89C99.2060500@free.fr> (raw)
In-Reply-To: <fa.8TBiwbgs8B881k+3X+IlFjhqpLI@ifi.uio.no>

[ Re-sending in the hope that it will be archived ]

Ingo Molnar wrote:

> John Stultz wrote:
> 
>> On Wed, 2007-01-24 at 10:41 +0100, John wrote:
>> 
>>> I'm using the POSIX timers API. My platform is x86 running Linux
>>> 2.6.18.6 patched with the high-resolution timer subsystem.
>>> 
>>> http://www.tglx.de/hrtimers.html
>>> 
>>> My process is the only SCHED_FIFO process on the system. There are 
>>> no user-space processes with a higher priority. AFAICT, only a 
>>> kernel thread could keep the CPU away from my app.
>>> 
>>> Is there a periodic kernel thread that runs every 2 seconds, cannot 
>>> be preempted, and runs for over 50 µs??
>> 
>> This sounds like a BIOS SMI issue. Can you reproduce this behavior on 
>> different hardware?
> 
> note that only the -hrt patchset is used - not the full -rt patchset
> - so 50 usecs delays (and more) are quite possible and common.

Ingo,

You are correct, I only used -hrt.
I will _definitely_ give -rt a try.

I am fully aware that an occasional 100 µs delay is possible, given a
soft real-time operating system. However, what I cannot explain is:

Why do these /occasional/ delays always happen a multiple of 2 seconds
apart? Can you explain this odd behavior?

> My question would be: does the same problem occur with the full -rt
> patchset and PREEMPT_RT? (see http://rt.wiki.kernel.org for details)

I will test on a different PC, as John suggested.
I will try the full -rt patchset in a few days.

+++++

On a related note, there is no -hrt patch for 2.6.19:
http://www.tglx.de/projects/hrtimers/
Is it because the patch for 2.6.19-rc4-mm1 applies cleanly to 2.6.19?

There is no -hrt patch for 2.6.20.
Has it been completely merged?

Regards.


  parent reply	other threads:[~2007-01-25 12:04 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <fa.NwnlFyMPfa3XG6my3HKGWnCW3x4@ifi.uio.no>
     [not found] ` <fa.Ji4GnAbBF2FR5JbSxvxn2haJZIk@ifi.uio.no>
2007-01-25  9:59   ` John
2007-01-25 22:19     ` john stultz
     [not found]   ` <fa.8TBiwbgs8B881k+3X+IlFjhqpLI@ifi.uio.no>
2007-01-25 12:03     ` John [this message]
     [not found] <fa.4zD54Ie6Ozt0P4YqQSicS+XzXGw@ifi.uio.no>
     [not found] ` <fa.G+/T32f2o1M3+YGLca/O8NaAQyY@ifi.uio.no>
     [not found]   ` <fa.6Ua8xjNfLKQEZZgDsoJgPMyww4g@ifi.uio.no>
     [not found]     ` <fa.yQlV+WU0TgrJTVqjopa01tgCnT0@ifi.uio.no>
     [not found]       ` <fa.ucVrLJ1Lh6FjdBHRglsIUc8/evk@ifi.uio.no>
     [not found]         ` <fa.Id9oufyELrVbe5Wb8SRakwC0V50@ifi.uio.no>
2007-02-01 10:18           ` John
2007-02-06 12:37             ` Ingo Molnar
2007-02-07 10:13               ` John
2007-02-05 16:37           ` John
2007-02-06  7:31             ` Peter Zijlstra
2007-02-07 10:25               ` John
2007-02-08 17:32                 ` Thomas Gleixner
2007-02-09 15:25                   ` John
2007-02-09 16:21                     ` Benedikt Spranger
2007-02-09 16:43                     ` Thomas Gleixner
     [not found] <fa.mtUvfgenNQkCc8835prYbwyiPQs@ifi.uio.no>
     [not found] ` <fa.lwkMc548uRMcUjd9KZ2pC1DMKT4@ifi.uio.no>
     [not found]   ` <fa.dTtI0ctv1nu+tCWiK6jGPnrX69k@ifi.uio.no>
     [not found]     ` <fa.CMU3scpnLxfHVWRFPcmfRl2CjhA@ifi.uio.no>
2007-01-30 17:38       ` John
2007-01-30 20:25         ` Ingo Molnar
     [not found] <45B729AF.4030701@privacy.net>
2007-01-24 19:02 ` john stultz
2007-01-24 20:09   ` Ingo Molnar

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