linux-kernel - Re: 2.6.19-rc5: known regressions

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Date:	Wed, 8 Nov 2006 17:22:02 +0100
From:	Adrian Bunk <bunk@...sta.de>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: 2.6.19-rc5: known regressions

On Wed, Nov 08, 2006 at 07:47:07AM -0800, Linus Torvalds wrote:
> 
> 
> On Wed, 8 Nov 2006, Eric W. Biederman wrote:
> > 
> > I haven't seen anyone reproduce this but Tim Chen, and Tim wasn't
> > able to root cause the problem so I believe we are going to have
> > this regression :(
> 
> Note that you really shouldn't look too closely at lmbench scheduling 
> fluctuations. They can fluctuate a _lot_, especially under SMP, and it can 
> depend on things like cache layout that has nothing to do with the 
> scheduler (ie just code movement can make the lmbench numbers change).
> 
> So there are "regressions" and there are "shit happens". It can sometimes 
> be hard to tell the two apart, of course ;)

There's perhaps one thing that might help us to see whether it's just a 
benchmark effekt or a real problem:

With Tim's CONFIG_NR_CPUS=8, NR_IRQS only increases from 224 in 2.6.18 
to 512 in 2.6.19-rc.

With CONFIG_NR_CPUS=255, NR_IRQS increases from 224 in 2.6.18
to 8416 in 2.6.19-rc.

@Tim:
Can you try CONFIG_NR_CPUS=255 with both 2.6.18 and 2.6.19-rc5?

> 		Linus

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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