Messages in this thread | | | Date | Tue, 11 Nov 2008 19:08:52 +0100 | From | Jens Axboe <> | Subject | Re: Slow file transfer speeds with CFQ IO scheduler in some cases |
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On Tue, Nov 11 2008, Jeff Moyer wrote: > Jens Axboe <jens.axboe@oracle.com> writes: > > > On Tue, Nov 11 2008, Jens Axboe wrote: > >> On Tue, Nov 11 2008, Jens Axboe wrote: > >> > On Mon, Nov 10 2008, Jeff Moyer wrote: > >> > > "Vitaly V. Bursov" <vitalyb@telenet.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@oracle.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@maiden ~]# mount megadeth:/export/cciss /mnt/megadeth/ > >> > > [root@maiden ~]# 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@maiden ~]# umount /mnt/megadeth/ > >> > > [root@maiden ~]# mount megadeth:/export/cciss /mnt/megadeth/ > >> > > [root@maiden ~]# 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@maiden ~]# 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. > > > > OK, found the issue. A few bugs there... cfq_prio_tree_lookup() doesn't > > even return a hit, since it just breaks and returns NULL always. That > > can cause cfq_prio_tree_add() to screw up the rbtree. The code to > > correct on ioprio change wasn't correct either, I changed that as well. > > New patch below, Vitaly can you give it a spin? > > Thanks for doing that! Yeah, that was a stupid bug with the lookup > routine. I don't know that I agree with you that the ioprio change code > was wrong. I looked at all of the callers and that seemed the code path > that was used for I/O priority *changes*. The initial creation was > already okay, wasn't it?
You only did it in cfq_prio_boost(), you should go one down and do it for all prio changes. cfq_init_prio_data() gets called to fix state up lazily when it notices a prio change, either due to prio boost or because someone ran ionice.
-- Jens Axboe
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