Messages in this thread | | | Subject | Re: tiobench read 50% regression with 2.6.30-rc1 | From | "Zhang, Yanmin" <> | Date | Wed, 15 Apr 2009 09:27:41 +0800 |
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On Tue, 2009-04-14 at 14:14 +0200, Jens Axboe wrote: > On Fri, Apr 10 2009, Zhang, Yanmin wrote: > > On Thu, 2009-04-09 at 11:57 +0200, Jens Axboe wrote: > > > 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
> > > > > > 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. > > I tried 4,8,16,64,128 and didn't find result difference. > > Can you try with this patch? The new patch does fix it.
> > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index a4809de..66f00e5 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -1905,10 +1905,17 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, > * Remember that we saw a request from this process, but > * don't start queuing just yet. Otherwise we risk seeing lots > * of tiny requests, because we disrupt the normal plugging > - * and merging. > + * and merging. If the request is already larger than a single > + * page, let it rip immediately. For that case we assume that > + * merging is already done. > */ > - if (cfq_cfqq_wait_request(cfqq)) > + if (cfq_cfqq_wait_request(cfqq)) { > + if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE) { > + del_timer(&cfqd->idle_slice_timer); > + blk_start_queueing(cfqd->queue); > + } > cfq_mark_cfqq_must_dispatch(cfqq); > + } > } else if (cfq_should_preempt(cfqd, cfqq, rq)) { > /* > * not the active queue - expire current slice if it is >
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