> -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of > Ilya Dryomov > Sent: 10 June 2015 16:23 > To: Nick Fisk > Cc: ceph-users > Subject: Re: krbd splitting large IO's into smaller IO's > > On Wed, Jun 10, 2015 at 6:18 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. > > Thanks, > > Ilya > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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