linux-kernel - Re: v2.6.21.5-rt19

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Message-Id: <1183935022.11854.17.camel@cmn3.stanford.edu>
Date:	Sun, 08 Jul 2007 15:50:22 -0700
From:	Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Rui Nuno Capela <rncbc@...bc.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	RT-Users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"jcaceres@...ma.Stanford.EDU" <jcaceres@...ma.Stanford.EDU>,
	Carsten Emde <carsten.emde@...dl.org>, nando@...ma.Stanford.EDU
Subject: Re: v2.6.21.5-rt19

On Sun, 2007-07-08 at 15:36 -0700, Fernando Lopez-Lezcano wrote:
> On Sat, 2007-07-07 at 11:24 +0200, Ingo Molnar wrote:
> > * Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU> wrote:
> > > > > Changes since 2.6.21.5-rt18:
> > > > >
> > > > > - Fixed a nasty and hard to track down slowness / boot problem on SMP
> > > > > machines with CONFIG_NOHZ enabled. The problem was caused by the timer
> > > > > wheel base lock held during the get_next_timer_interrupt() call in the
> > > > > idle path, which eventually led to a bogus PI boosting of the idle task
> > > > > and in consequence a stale wrong scheduler selection for the affected idle
> > > > > task.
> > > > >
> > > > > Kudos to Carsten Emde, who patiently and meticulously isolated the
> > > > > problem and provided the traces, which allowed to identify the root cause.
> > > > >
> > > > > Problem solution: Prevent idle task boosting
> > 
> > > > Maybe someone remember me whining about troubles with 2.6.21-rt2..18 
> > > > on my Core2 T7200 laptop (fujitsu-siemens amilo i1520).
> > > > 
> > > > Althought I'm still with my fingers crossed, I can tell the good 
> > > > news are that 2.6.21.5-rt19 (and -rt20) does behave far better now 
> > > > on the very same box.
> > > 
> > > Yes, it works much better indeed...
> > > 
> > > Ingo: is there a place where I can read about the changes in different 
> > > rtxx releases? What is new/better/fixed in rt20? (I see scheduler 
> > > stuff in a diff from rt19 to rt20 but I don't really know what it 
> > > means).
> > 
> > and rt18 was a -rt-only NOHZ fix, that bug got introduced in rt11 when 
> > CFS was merged.
> > 
> > i _think_ Rui might have seen two separate problems. Perhaps by the time 
> > we fixed the first problem (which Rui saw since -rt2) we introduced the 
> > other one via -rt11 - which then got fixed in -rt19.
> 
> Ahh, CFS is now part of rt, I was obviously not paying attention... I'm
> really trying to provide a "stable" rt kernel for audio usage and
> including another subsystem into rt is - IMHO - not going to help.
> What's the chance of splitting things?
> 
> > btw., we'd love to get more feedback regarding CFS. CFS is a completely 
> > new scheduler for Linux. 
> 
> Then I'd rather have it separate from rt. 

Please?

I would like to provide the least ammount of new functionality that is
really necessary in my audio kernels. Audio related requirements include
the rt patch but not a new scheduler. 

> > It has a design centered around keeping 
> > application latencies down, so it is ultimately real-time friendly, and 
> > it should also make things work better for desktop-ish and audio-ish 
> > stuff as well. (even under SCHED_OTHER)
> 
> Maybe this is CFS related? (tail of a thread in the Planet CCRMA mailing
> list):
> 
> On Sun, 2007-07-08 at 15:26 -0400, Hector Centeno wrote:
> > Ok, so just to confirm, that 2.6.21-0182.rt19.1.fc7.ccrmart works fine
> > on my desktop but on my laptop it makes Firefox and Tomboy to crash.
> > On the same laptop using 2.6.21-0182.rt17.1.fc7.ccrmart there is no
> > problem.

It looks to my untrained eye like it is CFS related, I'm attaching the
last part of the strace of firefox while it tries to load a flash site.
The firefox process is left in an unkillable (not even by -9) state.
What else could I provide to debug the problem? (this is in a T61 laptop
with the Intel 7700 processor). 

-- Fernando


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