linux-kernel - Re: Scheduler broken? sdhci issues with scheduling

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Date:	Fri, 29 Feb 2008 21:39:14 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Simon Huggins <huggie@...th.li>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Scheduler broken? sdhci issues with scheduling


* Simon Huggins <huggie@...th.li> wrote:

> Hi Ingo,
> 
> (please cc me again)
> 
> On Fri, Feb 29, 2008 at 02:34:33PM +0100, Ingo Molnar wrote:
> > * Simon Huggins <huggie@...th.li> wrote:
> > > [ Please Cc me on replies ]
> > > I had a bug with sdhci which Pierre Ossman looked at for me.
> > > In the end essentially the fix was to use HZ=1000 and nothing else. 
> > > Pierre seemed to think that this was a bug in the scheduler.
> > does the patch below help, even if you keep HZ=100? This doesnt look 
> > like a scheduler issue, it's more of a timer/timing issue. Different HZ 
> > means different msleep() results - and the mmc code does a loop of small 
> > msleep delays.
> 
> Thanks for looking at it.
> 
> I did tests with 2.6.24.3 with HZ=1000 and HZ=100 and as expected the
> latter didn't work.
> 
> > -------------->
> > ---
> >  drivers/mmc/core/core.h |    7 +------
> >  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> > Index: linux/drivers/mmc/core/core.h
> > ===================================================================
> > --- linux.orig/drivers/mmc/core/core.h
> > +++ linux/drivers/mmc/core/core.h
> > @@ -36,12 +36,7 @@ void mmc_set_timing(struct mmc_host *hos
> 
> >  static inline void mmc_delay(unsigned int ms)
> >  {
> > -	if (ms < 1000 / HZ) {
> > -		cond_resched();
> > -		mdelay(ms);
> > -	} else {
> > -		msleep(ms);
> > -	}
> > +	mdelay(ms);
> >  }
> 
> >  void mmc_rescan(struct work_struct *work);
> 
> That doesn't work.  I did a test with HZ=100 and this patch.  I've 
> attached the log as patch1-log.

> Anything else I can try?

so neither precise, nor imprecise timings help??

	Ingo
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