Messages in this thread | | | Date | Fri, 25 Dec 2009 11:16:27 +0100 | Subject | Re: cfq-iosched: tiobench regression | From | Corrado Zoccolo <> |
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Hi Shaohua, On Thu, Dec 24, 2009 at 1:55 AM, Shaohua Li <shaohua.li@intel.com> wrote: > df5fe3e8e13883f58dc97489076bbcc150789a21 > b3b6d0408c953524f979468562e7e210d8634150 > The coop merge is too aggressive. For example, if two tasks are reading two > files where the two files have some adjecent blocks, cfq will immediately > merge them. cfq_rq_close() also has trouble, sometimes the seek_mean is very > big. I did a test to make cfq_rq_close() always checks the distence according > to CIC_SEEK_THR, but still saw a lot of wrong merge. (BTW, why we take a long > distence far away request as close. Taking them close doesn't improve any thoughtput > to me. Maybe we should always use CIC_SEEK_THR as close criteria). Yes, when deciding if two queues are going to be merged, we should use the constant CIC_SEEK_THR. > So sounds we need make split more aggressive. But the split is too lazay, > which requires to wait 1s. Time based check isn't reliable as queue might not > run at given time, so uses a small time isn't ok. 1s is too much, but I wouldn't abandon a time based approach. To fix the problem of queue not being run, you can consider a slice. If at the end of the slice, the queue is seeky, you split it.
> I'm thinking changing the split > check based on requests number instead of time. That is if several continuous > requests are regarded as seeky, the coop queue is split. See blow RFC patch. > How many count a queue should be split after need more consideration, > below patch just uses an arbitary number. This reduce about 5% performance > lost when doing tio 32 threads sequential read.
Thanks, Corrado -- __________________________________________________________________________
dott. Corrado Zoccolo mailto:czoccolo@gmail.com PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- -- 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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