Re: Putrid Elevator Behavior 2.4.18/19

[Jeff V. Merkey]

> > 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
> 

Andrew,

I have been running a test run against 2.4.19-pre4 (and later) for 
over a week non-stop and the elevator problem appears to have been 
corrected by this fix.  I will update further if the problem 
resurfaces.

:-)

Jeff