Andrew Morton wrote:

>Con Kolivas wrote:
>
>>Note the significant discrepancy between mm1 and mm3. This reminds me of what
>>happened last time I enabled shared 3rd level pagetables - Andrew do you want
>>me to do a set of numbers with this disabled?
>>
>
>That certainly couldn't hurt.  But your tests are, in general, tesging
>the IO scheduler.  And the IO scheduler has changed radically in each
>of the recent -mm's.
>
>So testing with rbtree-iosched reverted would really be the only way
>to draw comparisons on how the rest of the code is behaving.
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Andrew there is, in fact a problem with the io scheduler in mm3 as far
as I can see. Jens is away 'till Monday so he hasn't confirmed this yet.
Basically if the device can't get through the entire queue within the
read|write_expire timeout, they will start being submitted in fifo order
slowing down the device more (probably) and contributing to the problem.
It may be causing the bad numbers in contest. Here is a patch which
relieves the problem for loads I am testing (bench.c, tiobench).

Con, it would be nice if you could try this, if you value your disk,
maybe you could wait for Jens to get back!

Regards,
Nick Piggin