On Wed, Jun 10, 2015 at 7:04 PM, Nick Fisk <nick@xxxxxxxxxx> wrote: >> > >> -----Original Message----- >> > >> From: Ilya Dryomov [mailto:idryomov@xxxxxxxxx] >> > >> Sent: 10 June 2015 14:06 >> > >> To: Nick Fisk >> > >> Cc: ceph-users >> > >> Subject: Re: krbd splitting large IO's into smaller >> > >> IO's >> > >> >> > >> On Wed, Jun 10, 2015 at 2:47 PM, Nick Fisk <nick@xxxxxxxxxx> wrote: >> > >> > Hi, >> > >> > >> > >> > Using Kernel RBD client with Kernel 4.03 (I have also tried some >> > >> > older kernels with the same effect) and IO is being split into >> > >> > smaller IO's which is having a negative impact on performance. >> > >> > >> > >> > cat /sys/block/sdc/queue/max_hw_sectors_kb >> > >> > 4096 >> > >> > >> > >> > cat /sys/block/rbd0/queue/max_sectors_kb >> > >> > 4096 >> > >> > >> > >> > Using DD >> > >> > dd if=/dev/rbd0 of=/dev/null bs=4M >> > >> > >> > >> > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s >> avgrq-sz >> > >> > avgqu-sz await r_await w_await svctm %util >> > >> > rbd0 0.00 0.00 201.50 0.00 25792.00 0.00 >> 256.00 >> > >> > 1.99 10.15 10.15 0.00 4.96 100.00 >> > >> > >> > >> > >> > >> > Using FIO with 4M blocks >> > >> > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s >> avgrq-sz >> > >> > avgqu-sz await r_await w_await svctm %util >> > >> > rbd0 0.00 0.00 232.00 0.00 118784.00 0.00 >> 1024.00 >> > >> > 11.29 48.58 48.58 0.00 4.31 100.00 >> > >> > >> > >> > Any ideas why IO sizes are limited to 128k (256 blocks) in DD's >> > >> > case and 512k in Fio's case? >> > >> >> > >> 128k vs 512k is probably buffered vs direct IO - add iflag=direct >> > >> to your dd invocation. >> > > >> > > Yes, thanks for this, that was the case >> > > >> > >> >> > >> As for the 512k - I'm pretty sure it's a regression in our switch >> > >> to blk-mq. I tested it around 3.18-3.19 and saw steady 4M IOs. I >> > >> hope we are just missing a knob - I'll take a look. >> > > >> > > I've tested both 4.03 and 3.16 and both seem to be split into 512k. >> > > Let >> me >> > know if you need me to test any other particular version. >> > >> > With 3.16 you are going to need to adjust max_hw_sectors_kb / >> > max_sectors_kb as discussed in Dan's thread. The patch that fixed >> > that in the block layer went into 3.19, blk-mq into 4.0 - try 3.19. >> >> Sorry should have mentioned, I had adjusted both of them on the 3.16 >> kernel to 4096. >> I will try 3.19 and let you know. > > Better with 3.19, but should I not be seeing around 8192, or am I getting my > blocks and bytes mixed up? > > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz > avgqu-sz await r_await w_await svctm %util > rbd0 72.00 0.00 24.00 0.00 49152.00 0.00 4096.00 > 1.96 82.67 82.67 0.00 41.58 99.80 I'd expect 8192. I'm getting a box for investigation. Thanks, Ilya _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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