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From: Duncan Sands <duncan.sands@math.u-psud.fr>
To: Andrew Morton <akpm@digeo.com>
Subject: Re: fsync 50 times slower after 2.5.27
Date: Fri, 20 Sep 2002 14:15:12 +0200
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On Thursday 19 September 2002 23:22, Andrew Morton wrote:
> > OK!  This seems to fix the problem for 2.5.36.  I will also
> > test it for 2.5.34 since I didn't test 2.5.36 as rigourously
> > as 2.5.34 for the presence of the problem without the patch.
>
> (I dragged you back onto the mailing list)

No problem.

> Thanks for testing.  The semantics of sched_yield() have changed
> significantly in 2.5.  Probably correctly, but it is breaking a
> few things which were tuned for the old semantics.  Amongst those
> things are OpenOffice and, it seems, ext3 transaction batching.

Thanks for solving!  By the way, what does
                        set_current_state(TASK_RUNNING);
                        schedule();
actually do?  I guess it lets higher priority tasks have a go, while the
original yield() let equal priority tasks go first?  My knowledge of
sched_yield is out of date...

> The transaction batching does good things under some situations,
> and we want it to keep working.  I'll sit tight for the while, see
> where shed_yield() behaviour ends up.  If we still have a problem
> then probably a schedule_timeout(1) in there would suffice.
>
> > I will also test using ext2 (does ext2 use transaction.c?).
>
> No. ext2 will not exhibit this problem.

You are right.  I was confused because I thought I had observed
this problem once with ext2, but in fact I didn't test this case properly.
That's what you get for wanting to get some sleep at night...

Thanks again,

Duncan.
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