Re: Putrid Elevator Behavior 2.4.18/19

["Jeff V. Merkey" <jmerkey@vger.timpanogas.org>]

On Wed, Mar 20, 2002 at 05:22:18PM -0800, Andrew Morton wrote:
> "Jeff V. Merkey" wrote:
> > 
> > ...
> > > I will comply.  I tested with pre-3 patches and still saw this problem??
> > > Let me go and check the patches I applied to verify, I may not have
> > > applied the correct patch.
> > >
> > > Jeff
> > 
> > I verified we were using a stock 2.4.18 kernel on the specific system
> > without the pre-3 patches installed.  We have been testing with the
> > latest patches but not on this system.  We will apply and retest and
> > I will verify.
> > 
> 
> The elevator starvation change went into 2.4.19-pre1 I think.
> It shouldn't affect the problem which you've described - that
> change improved the situation where tasks were sleeping for
> long periods when they want to insert new requests.  But the
> problem which you're observing appears to affect already-inserted
> requests.
> 
> "Several minutes" is downright odd.  From your description
> it seems that all the requests are writes, but some of the
> writes (at a remote end of the disk) are being bypassed far
> too many times.
> 
> The bypass count _is_ tunable.  Although it sounds like the logic
> has come unstuck in some manner, it would be interesting if
> changing the elevator latency parameters for that queue affected
> the situation.
> 
> Have you experimented with `elvtune -r NNN /dev/foo' and
> `elvtune -w NNN /dev/foo'?

No, but I will test this tonight.  I am in tonight working on 
this problem until I run it down.

Jeff


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