Messages in this thread | | | Date | Fri, 21 May 2004 18:40:25 +1000 | From | Nick Piggin <> | Subject | Re: Random file I/O regressions in 2.6 [patch+results] |
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Jens Axboe wrote: > On Fri, May 21 2004, Nick Piggin wrote: > >>Andrew Morton wrote: >> >> >>>Open questions are: >>> >>>a) Why is 2.6 write coalescing so superior to 2.4? >>> >>>b) Why is 2.6 issuing more read requests, for less data? >>> >>>c) Why is Alexey seeing dissimilar results? >>> >> >> >>Interesting. I am not too familiar with 2.4's IO scheduler, >>but 2.6's have pretty comprehensive merging systems. Could >>that be helping, Jens? Or is 2.4 pretty equivalent? > > > 2.4 will give up merging faster than 2.6, elevator_linus will stop > looking for a merge point if the sequence drops to zero. 2.6 will always > merge. So that could explain the fewer writes. >
Yep OK, that could be one thing.
> >>What about things like maximum request size for 2.4 vs 2.6 >>for example? This is another thing that can have an impact, >>especially for writes. > > > I think that's pretty similar. Andrew didn't say what device he was > testing on, but 2.4 ide defaults to max 64k where 2.6 defaults to 128k. >
This could be another. If Andrew's using IDE, this alone could make up the entire difference *if* writes are nicely sequential. I guess they probably aren't, but it could still help. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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