Messages in this thread | | | Subject | Re: [patch]cfq-iosched: don't idle if a deep seek queue is slow | From | Shaohua Li <> | Date | Tue, 21 Sep 2010 07:55:07 +0800 |
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On Mon, 2010-09-20 at 22:15 +0800, Vivek Goyal wrote: > On Mon, Sep 20, 2010 at 04:53:34PM +0800, Shaohua Li wrote: > > If a deep seek queue slowly deliver requests but disk is much faster, idle > > for the queue just wastes disk throughput. If the queue delevers all requests > > before half its slice is used, the patch disable idle for it. > > In my test, application delivers 32 requests one time, the disk can accept > > 128 requests at maxium and disk is fast. without the patch, the throughput > > is just around 30m/s, while with it, the speed is about 80m/s. The disk is > > a SSD, but is detected as a rotational disk. I can configure it as SSD, but > > I thought the deep seek queue logic should be fixed too, for example, > > considering a fast raid. > > > > Hi Shaohua, > > So you seem to be addressing the issue of storage being fast enough and > a single queue not being able to keep the storage busy. > > But we have the same issue for non-deep queues for a fast storage. This > patch will not solve that. right.
> I think CFQ idling in general is a problem on faster storage. For SSDs we > can statically detect non-rotational media and disable idling. For faster > RAIDs we need to find an intellligent way of detection and disable idling. > > One of the suggestions at this year's LSF was to keep idling on only for > SATA disks and for any SCSI disks we can think of disabling idling by > default. May be with the help of udev rule. That makes sense, but shouldn't kernel has some reasonable setting? completely depending on userspace isn't reliable.
Thanks, Shaohua
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