From: Alistair John Strachan <s0348365@sms.ed.ac.uk>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Realtime Preemption, 2.6.12, Beginners Guide?
Date: Wed, 6 Jul 2005 18:14:23 +0100 [thread overview]
Message-ID: <200507061814.23656.s0348365@sms.ed.ac.uk> (raw)
In-Reply-To: <20050706170158.GA27797@elte.hu>
On Wednesday 06 Jul 2005 18:01, Ingo Molnar wrote:
> * Alistair John Strachan <s0348365@sms.ed.ac.uk> wrote:
> > > I'm beginning to understand the issue, and I see why you think the
> > > proposed patch fixes it. I'll compile and boot V0.7.51-05 now.
> >
> > Indeed, this seems to have fixed it.
> >
> > ( softirq-timer/0-3 |#0): new 8 us maximum-latency wakeup.
> > ( softirq-timer/0-3 |#0): new 9 us maximum-latency wakeup.
> > ( softirq-timer/0-3 |#0): new 9 us maximum-latency wakeup.
> > ( softirq-timer/0-3 |#0): new 9 us maximum-latency wakeup.
> > ( softirq-timer/0-3 |#0): new 10 us maximum-latency wakeup.
> > ( softirq-timer/0-3 |#0): new 14 us maximum-latency wakeup.
>
> great! Do the softlockup warnings still occur?
Yes, but in no greater a number.
[root] 18:09 [~] uptime
18:09:39 up 19 min, 4 users, load average: 0.36, 0.29, 0.16
[root] 18:09 [~] dmesg | grep BUG: | wc -l
5
So far, however, there have been no lockups! The previous kernels would die
very obviously within a couple of minutes.
I wonder if the ACPI problem was causing lockups (one thought I had was that
the "ondemand" cpufreq governor was generating more ACPI events than usual,
as the BIOS stepped through the different CPU speeds).
>
> > Find attached another trace (only 33us this time).
>
> the main latency comes from here:
> > <...>-3485 0Dnh2 13us : enqueue_task (__schedule)
> > <...>-3485 0Dnh2 14us+: trace_array (__schedule)
> > <...>-3485 0Dnh2 18us : trace_array <softirq--3> (69 6e)
> > <...>-3485 0Dnh2 18us : trace_array <<...>-3485> (76 78)
> > <...>-3485 0Dnh2 20us+: trace_array (__schedule)
> > softirq--3 0Dnh2 28us+: __switch_to (__schedule)
>
> trace_array() can be quite expensive (it generates a trace entry of
> every runnable task, with interrupts and preemption disabled). It is
> disabled if RT_DEADLOCK_DETECT is disabled. For pure wakeup latency
> tracing, the most optimal combination of options is:
>
[snip]
>
> such a kernel will still be able to generate /proc/latency_trace traces,
> but has much lower runtime overhead than your current kernel. (But you
> should probably keep all debugging enabled until all of the current
> problems have been resolved.)
>
> Ingo
Well, thanks for the info. As you said, when the remaining issues have been
resolved, I'll need to step up to a more efficient kernel, because I require
extremely low kernel latency for the software I'm writing (this was not an
idle patch fest).
--
Cheers,
Alistair.
personal: alistair()devzero!co!uk
university: s0348365()sms!ed!ac!uk
student: CS/CSim Undergraduate
contact: 1F2 55 South Clerk Street,
Edinburgh. EH8 9PP.
next prev parent reply other threads:[~2005-07-07 0:23 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-06 11:57 Realtime Preemption, 2.6.12, Beginners Guide? Alistair John Strachan
2005-07-06 12:51 ` Alistair John Strachan
2005-07-06 13:39 ` Ingo Molnar
2005-07-06 15:58 ` Alistair John Strachan
2005-07-06 16:28 ` Ingo Molnar
2005-07-06 16:31 ` Alistair John Strachan
2005-07-06 13:31 ` Ingo Molnar
2005-07-06 15:55 ` Alistair John Strachan
2005-07-06 16:24 ` Ingo Molnar
2005-07-06 16:37 ` Alistair John Strachan
2005-07-06 16:56 ` Alistair John Strachan
2005-07-06 17:01 ` Ingo Molnar
2005-07-06 17:14 ` Alistair John Strachan [this message]
2005-07-06 17:27 ` Ingo Molnar
2005-07-06 18:23 ` Alistair John Strachan
2005-07-06 18:38 ` Ingo Molnar
2005-07-06 18:41 ` Ingo Molnar
2005-07-06 19:47 ` Alistair John Strachan
2005-07-06 20:44 ` Ingo Molnar
2005-07-06 21:00 ` Alistair John Strachan
2005-07-06 21:02 ` Ingo Molnar
2005-07-06 22:15 ` Alistair John Strachan
2005-07-06 23:08 ` Fernando Lopez-Lezcano
2005-07-07 6:04 ` Michal Schmidt
2005-07-07 10:25 ` Ingo Molnar
2005-07-07 9:46 ` Alistair John Strachan
2005-07-07 11:21 ` Alistair John Strachan
2005-07-07 11:29 ` Ingo Molnar
2005-07-07 11:37 ` Alistair John Strachan
2005-07-07 11:42 ` Ingo Molnar
2005-07-07 12:15 ` Alistair John Strachan
2005-07-07 12:29 ` Ingo Molnar
2005-07-07 13:38 ` Alistair John Strachan
2005-07-07 12:33 ` Alistair John Strachan
2005-07-08 9:47 ` Alistair John Strachan
2005-07-08 11:46 ` Ingo Molnar
2005-07-08 18:38 ` Alistair John Strachan
2005-07-08 19:12 ` USB storage does not work with 3GB of RAM, but does with 2G of RAM Jon Schindler
2005-07-08 19:25 ` Realtime Preemption, 2.6.12, Beginners Guide? Ingo Molnar
2005-07-08 19:31 ` Ingo Molnar
2005-07-08 19:34 ` Ingo Molnar
2005-07-08 19:48 ` Ingo Molnar
2005-07-08 19:55 ` Alistair John Strachan
2005-07-08 20:45 ` Alistair John Strachan
2005-07-09 11:58 ` Ingo Molnar
2005-07-09 14:07 ` Alistair John Strachan
2005-07-09 14:55 ` Ingo Molnar
2005-07-09 15:57 ` Ingo Molnar
2005-07-09 16:02 ` Ingo Molnar
2005-07-09 16:04 ` Alistair John Strachan
2005-07-11 13:55 ` Alistair John Strachan
2005-07-11 14:12 ` Ingo Molnar
2005-07-11 14:16 ` Ingo Molnar
2005-07-11 14:38 ` Alistair John Strachan
2005-07-11 14:43 ` Ingo Molnar
2005-07-11 15:50 ` Alistair John Strachan
2005-07-13 14:45 ` Ingo Molnar
2005-07-13 15:30 ` Ingo Molnar
2005-07-14 19:58 ` Alistair John Strachan
2005-07-14 20:16 ` Lee Revell
2005-07-15 22:12 ` Alistair John Strachan
2005-07-12 2:56 ` Lee Revell
2005-07-11 15:07 ` Ingo Molnar
2005-07-12 20:09 ` Lee Revell
2005-07-12 21:01 ` Chuck Harding
2005-07-13 10:39 ` Ingo Molnar
2005-07-13 12:29 ` Gene Heskett
2005-07-13 14:01 ` K.R. Foley
2005-07-13 19:41 ` Chuck Harding
2005-07-13 19:45 ` Ingo Molnar
2005-07-14 13:39 ` K.R. Foley
2005-07-14 12:50 ` Karsten Wiese
2005-07-14 13:56 ` K.R. Foley
2005-07-14 14:10 ` K.R. Foley
2005-07-14 14:11 ` K.R. Foley
2005-07-14 19:49 ` Chuck Harding
2005-07-16 17:15 ` Ingo Molnar
2005-07-16 19:01 ` K.R. Foley
2005-07-17 12:07 ` Karsten Wiese
2005-07-18 15:46 ` K.R. Foley
2005-07-19 11:14 ` Karsten Wiese
2005-07-19 13:35 ` Gene Heskett
2005-07-19 13:57 ` Ingo Molnar
2005-07-19 15:19 ` Gene Heskett
2005-07-19 23:00 ` Karsten Wiese
2005-07-09 12:41 ` Ingo Molnar
2005-07-09 12:46 ` Ingo Molnar
2005-07-09 13:05 ` Ingo Molnar
2005-07-11 22:48 ` William Weston
2005-07-12 13:53 ` Ingo Molnar
2005-07-09 13:13 ` Ingo Molnar
2005-07-09 13:26 ` Ingo Molnar
2005-07-10 19:01 ` PCMCIA stack reduction patch [Was: Re: Realtime Preemption, 2.6.12, Beginners Guide?] Dominik Brodowski
2005-07-09 13:36 ` Realtime Preemption, 2.6.12, Beginners Guide? Ingo Molnar
2005-07-11 13:28 ` Paulo Marques
2005-07-08 11:48 ` Ingo Molnar
2005-07-08 17:42 ` Alistair John Strachan
2005-07-08 17:48 ` Jakub Jelinek
2005-07-08 18:12 ` Alistair John Strachan
[not found] <20050713063310.GA12661@elte.hu>
2005-07-13 10:30 ` karsten wiese
2005-07-13 18:38 ` Chuck Harding
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