Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-6

From: Mark_H_Johnson@raytheon.com
To: Ingo Molnar <mingo@elte.hu>
Cc: Amit Shah <amit.shah@codito.com>,
	Karsten Wiese <annabellesgarden@yahoo.de>,
	Bill Huey <bhuey@lnxw.com>, Adam Heath <doogie@debian.org>,
	emann@mrv.com, Gunther Persoons <gunther_persoons@spymac.com>,
	"K.R. Foley" <kr@cybsft.com>,
	linux-kernel@vger.kernel.org,
	Florian Schmidt <mista.tapas@gmx.net>,
	Fernando Pablo Lopez-Lezcano <nando@ccrma.Stanford.EDU>,
	Lee Revell <rlrevell@joe-job.com>,
	Rui Nuno Capela <rncbc@rncbc.org>,
	Shane Shrybman <shrybman@aei.ca>,
	Esben Nielsen <simlo@phys.au.dk>,
	Thomas Gleixner <tglx@linutronix.de>,
	Michal Schmidt <xschmi00@stud.feec.vutbr.cz>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-6
Date: Thu, 9 Dec 2004 12:15:41 -0600	[thread overview]
Message-ID: <OF005FDB8A.72F792AC-ON86256F65.0063E013@raytheon.com> (raw)

>* Mark_H_Johnson@raytheon.com <Mark_H_Johnson@raytheon.com> wrote:
>
>> >also, i'd like to take a look at latency traces, if you have them for
>> >this run.
>>
>> I could if I had any. The _RT run had NO latency traces > 250 usec
>> (the limit I had set for the test). The equivalent _PK run had 37 of
>> those traces. I can rerun the test with a smaller limit to get some if
>> it is really important. My build of -12 is almost done and we can see
>> what kind of repeatability / results from the all_cpus trace shows.
>
>/me is puzzled.
>
>so all the CPU-loop delays within the -RT kernel are below 250 usecs? I
>guess i dont understand what this means then:

There were no cases where /proc/sys/kernel/preempt_max_latency went
over 250 usec in the RT stress test that I did (for the same test, _PK
had over 30 such traces).

>| The max CPU latencies in RT are worse than PK as well. The values for
>| RT range from 3.00 msec to 5.43 msec and on PK range from 1.45 msec to
>| 2.24 msec.
>
>these come from userspace timestamping? So where userspace detects a
>delay the kernel tracer doesnt measure any?
Yes. That is correct. Very puzzling to me too.

--Mark H Johnson
  <mailto:Mark_H_Johnson@raytheon.com>