Messages in this thread | | | Date | Thu, 9 Apr 2009 11:57:06 +0200 | From | Jens Axboe <> | Subject | Re: tiobench read 50% regression with 2.6.30-rc1 |
| |
On Thu, Apr 09 2009, Zhang, Yanmin wrote: > Comparing with 2.6.29's result, tiobench (read) has about 50% regression > with 2.6.30-rc1 on all my machines. Bisect down to below patch. > > b029195dda0129b427c6e579a3bb3ae752da3a93 is first bad commit > commit b029195dda0129b427c6e579a3bb3ae752da3a93 > Author: Jens Axboe <jens.axboe@oracle.com> > Date: Tue Apr 7 11:38:31 2009 +0200 > > cfq-iosched: don't let idling interfere with plugging > > When CFQ is waiting for a new request from a process, currently it'll > immediately restart queuing when it sees such a request. This doesn't > work very well with streamed IO, since we then end up splitting IO > that would otherwise have been merged nicely. For a simple dd test, > this causes 10x as many requests to be issued as we should have. > Normally this goes unnoticed due to the low overhead of requests > at the device side, but some hardware is very sensitive to request > sizes and there it can cause big slow downs. > > > > Command to start the testing: > #tiotest -k0 -k1 -k3 -f 80 -t 32 > > It's a multi-threaded program and starts 32 threads. Every thread does I/O > on its own 80MB file.
It's not a huge surprise that we regressed there. I'll get this fixed up next week. Can you I talk you into trying to change the 'quantum' sysfs variable for the drive? It's in /sys/block/xxx/queue/iosched where xxx is your drive(s). It's set to 4, if you could try progressively larger settings and retest, that would help get things started.
Thanks!
-- Jens Axboe
| |