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SubjectRe: Terrible elevator performance in kernel 2.4.0-test8
Date
In article <Pine.LNX.4.21.0009141152480.1413-200000@elte.hu>,
Ingo Molnar <mingo@elte.hu> wrote:
>
>i'm seeing similar problems. I think these problems started when the
>elevator was rewritten, i believe it broke the proper unplugging of IO
>devices. Does your performance problem get fixed by the attached
>workaround?

If this helps, that implies that somebody is doing a (critical) IO
request, without ever actually asking for the request to be _started_.

That sounds like a bug, and the patch looks like band-aid.

Where do we end up scheduling without starting the disk IO?

I'd rather add the disk schedule to _that_ place, instead of adding it
to every re-schedule event.

(For example, on a multi-CPU system it should _not_ be the case that one
CPU scheduling frequently should cause IO performance to go down - yet
your patch will do exactly that).

Could you make it print out a backtrace instead when this happens (make
it do it for the first few times, so as not to flood your console
forever if it ends up being common..)

Linus
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