Re: Process Scheduling Issue using sg/libata

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On 11/16/07, Tejun Heo <htejun@xxxxxxxxx> wrote:
> Fajun Chen wrote:
> > I use sg/libata and ata pass through for read/writes. Linux 2.6.18-rc2
> > and libata version 2.00 are loaded on ARM XScale board.  Under heavy
> > cpu load (e.g. when blocks per transfer/sector count is set to 1),
> > I've observed that the test application can suck cpu away for long
> > time (more than 20 seconds) and other processes including high
> > priority shell can not get the time slice to run.  What's interesting
> > is that if the application is under heavy IO load (e.g. when blocks
> > per transfer/sector count is set to 256),  the problem goes away. I
> > also tested with open source code sg_utils and got the same result, so
> > this is not a problem specific to my user-space application.
> >
> > Since user preemption is checked when the kernel is about to return to
> > user-space from a system call,  process scheduler should be invoked
> > after each system call. Something seems to be broken here.  I found a
> > similar issue below:
> > http://marc.info/?l=linux-arm-kernel&m=103121214521819&w=2
> > But that turns out to be an issue with MTD/JFFS2 drivers, which are
> > not used in my system.
> >
> > Has anyone experienced similar issues with sg/libata? Any information
> > would be greatly appreciated.
>
> That's one weird story.  Does kernel say anything during that 20 seconds?
>
No. Nothing in kernel log.

Fajun
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