Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: Slow file transfer speeds with CFQ IO scheduler in some cases | Date | Mon, 10 Nov 2008 08:51:18 -0500 |
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Jens Axboe <jens.axboe@oracle.com> writes:
> On Sun, Nov 09 2008, Vitaly V. Bursov wrote: >> Hello, >> >> I'm building small server system with openvz kernel and have ran into >> some IO performance problems. Reading a single file via NFS delivers >> around 9 MB/s over gigabit network, but while reading, say, 2 different >> or same file 2 times at the same time I get >60MB/s. >> >> Changing IO scheduler to deadline or anticipatory fixes problem. >> >> Tested kernels: >> OpenVZ RHEL5 028stab059.3 (9 MB/s with HZ=100, 20MB/s with HZ=1000 >> fast local reads) >> Vanilla 2.6.27.5 (40 MB/s with HZ=100, slow local reads) >> >> Vanilla performs better in worst case but I believe 40 is still low >> concerning test results below. > > Can you check with this patch applied? > > http://bugzilla.kernel.org/attachment.cgi?id=18473&action=view
Funny, I was going to ask the same question. ;) The reason Jens wants you to try this patch is that nfsd may be farming off the I/O requests to different threads which are then performing interleaved I/O. The above patch tries to detect this and allow cooperating processes to get disk time instead of waiting for the idle timeout.
Cheers,
Jeff
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