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Date: Tue, 11 Nov 2008 10:35:40 +0100 From: Jens Axboe <jens.axboe@...cle.com> To: Jeff Moyer <jmoyer@...hat.com> Cc: "Vitaly V. Bursov" <vitalyb@...enet.dn.ua>, linux-kernel@...r.kernel.org Subject: Re: Slow file transfer speeds with CFQ IO scheduler in some cases On Tue, Nov 11 2008, Jens Axboe wrote: > On Mon, Nov 10 2008, Jeff Moyer wrote: > > "Vitaly V. Bursov" <vitalyb@...enet.dn.ua> writes: > > > > > Jens Axboe wrote: > > >> On Mon, Nov 10 2008, Vitaly V. Bursov wrote: > > >>> Jens Axboe wrote: > > >>>> On Mon, Nov 10 2008, Jeff Moyer wrote: > > >>>>> Jens Axboe <jens.axboe@...cle.com> writes: > > >>>>> > > >>>>>> 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. > > >>>> Precisely :-) > > >>>> > > >>>> The only reason I haven't merged it yet is because of worry of extra > > >>>> cost, but I'll throw some SSD love at it and see how it turns out. > > >>>> > > >>> Sorry, but I get "oops" same moment nfs read transfer starts. > > >>> I can get directory list via nfs, read files locally (not > > >>> carefully tested, though) > > >>> > > >>> Dumps captured via netconsole, so these may not be completely accurate > > >>> but hopefully will give a hint. > > >> > > >> Interesting, strange how that hasn't triggered here. Or perhaps the > > >> version that Jeff posted isn't the one I tried. Anyway, search for: > > >> > > >> RB_CLEAR_NODE(&cfqq->rb_node); > > >> > > >> and add a > > >> > > >> RB_CLEAR_NODE(&cfqq->prio_node); > > >> > > >> just below that. It's in cfq_find_alloc_queue(). I think that should fix > > >> it. > > >> > > > > > > Same problem. > > > > > > I did make clean; make -j3; sync; on (2 times) patched kernel and it went OK > > > but It won't boot anymore with cfq with same error... > > > > > > Switching cfq io scheduler at runtime (booting with "as") appears to work with > > > two parallel local dd reads. > > > > Strange, I can't reproduce a failure. I'll keep trying. For now, these > > are the results I see: > > > > [root@...den ~]# mount megadeth:/export/cciss /mnt/megadeth/ > > [root@...den ~]# dd if=/mnt/megadeth/file1 of=/dev/null bs=1M > > 1024+0 records in > > 1024+0 records out > > 1073741824 bytes (1.1 GB) copied, 26.8128 s, 40.0 MB/s > > [root@...den ~]# umount /mnt/megadeth/ > > [root@...den ~]# mount megadeth:/export/cciss /mnt/megadeth/ > > [root@...den ~]# dd if=/mnt/megadeth/file1 of=/dev/null bs=1M > > 1024+0 records in > > 1024+0 records out > > 1073741824 bytes (1.1 GB) copied, 23.7025 s, 45.3 MB/s > > [root@...den ~]# umount /mnt/megadeth/ > > > > Here is the patch, with the suggestion from Jens to switch the cfqq to > > the right priority tree when the priority is changed. > > I don't see the issue here either. Vitaly, are you using any openvz > kernel patches? IIRC, they patch cfq so it could just be that your cfq > version is incompatible with Jeff's patch. Heh, got it to trigger about 3 seconds after sending that email! I'll look more into it. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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