Messages in this thread | | | Date | Tue, 11 Nov 2008 18:53:24 +0200 | From | "Vitaly V. Bursov" <> | Subject | Re: Slow file transfer speeds with CFQ IO scheduler in some cases |
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Jens Axboe wrote: > 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? >
No crashes so far. Transfer speed is quiet good also.
NFS+deadline, file not cached:
avg-cpu: %user %nice %system %iowait %steal %idle 0,00 0,00 25,50 19,40 0,00 55,10
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sda 6648,80 0,00 1281,70 0,00 115179,20 0,00 89,86 5,35 4,18 0,35 45,20 sdb 6672,30 0,00 1257,00 0,00 115292,80 0,00 91,72 5,09 4,06 0,35 44,60
NFS+cfq, file not cached:
avg-cpu: %user %nice %system %iowait %steal %idle 0,05 0,00 25,30 23,95 0,00 50,70
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sda 6403,00 0,00 1089,90 0,00 108655,20 0,00 99,69 4,50 4,13 0,41 44,50 sdb 6394,90 0,00 1099,60 0,00 108639,20 0,00 98,80 4,53 4,12 0,39 42,50
Just for reference: 10 sec interval average, gigabit network, no tcp/udp hardware checksumming may lead to high system cpu load.
Also, a few more test (server has 4G RAM):
NFS+cfq, file not cached: $ dd if=test of=/dev/null bs=1M count=2000 2000+0 records in 2000+0 records out 2097152000 bytes (2.1 GB) copied, 24.9147 s, 84.2 MB/s
NFS+deadline, file not cached: 2000+0 records in 2000+0 records out 2097152000 bytes (2.1 GB) copied, 23.2999 s, 90.0 MB/s
file cached on server: 2000+0 records in 2000+0 records out 2097152000 bytes (2.1 GB) copied, 21.9784 s, 95.4 MB/s
Local single dd read leads to 193 MB/s for deadline and 167 MB/s for cfq.
-- Thanks, Vitaly
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