Messages in this thread | | | Date | Mon, 28 Dec 2009 16:46:59 +0800 | From | Shaohua Li <> | Subject | Re: [PATCH]cfq-iosched: don't take requests with long distence as close |
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On Mon, Dec 28, 2009 at 04:36:39PM +0800, Corrado Zoccolo wrote: > Hi Shaohua, > On Mon, Dec 28, 2009 at 3:03 AM, Shaohua Li <shaohua.li@intel.com> wrote: > > On Fri, Dec 25, 2009 at 06:16:27PM +0800, Corrado Zoccolo wrote: > >> Hi Shaohua, > >> On Thu, Dec 24, 2009 at 1:55 AM, Shaohua Li <shaohua.li@intel.com> wrote: > >> > df5fe3e8e13883f58dc97489076bbcc150789a21 > >> > b3b6d0408c953524f979468562e7e210d8634150 > >> > The coop merge is too aggressive. For example, if two tasks are reading two > >> > files where the two files have some adjecent blocks, cfq will immediately > >> > merge them. cfq_rq_close() also has trouble, sometimes the seek_mean is very > >> > big. I did a test to make cfq_rq_close() always checks the distence according > >> > to CIC_SEEK_THR, but still saw a lot of wrong merge. (BTW, why we take a long > >> > distence far away request as close. Taking them close doesn't improve any thoughtput > >> > to me. Maybe we should always use CIC_SEEK_THR as close criteria). > >> Yes, when deciding if two queues are going to be merged, we should use > >> the constant CIC_SEEK_THR. > > > > seek_mean could be very big sometimes, using it as close criteria is meanless > > as this doen't improve any performance. So if it's big, let's fallback to > > default value. > > meanless -> meaningless (also in the comment within code) oops
> > Signed-off-by: Shaohua Li<shaohua.li@intel.com> > > > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > > index e2f8046..8025605 100644 > > --- a/block/cfq-iosched.c > > +++ b/block/cfq-iosched.c > > @@ -1682,6 +1682,10 @@ static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq, > > if (!sample_valid(cfqq->seek_samples)) > > sdist = CFQQ_SEEK_THR; > > > > + /* if seek_mean is big, using it as close criteria is meanless */ > > + if (sdist > CFQQ_SEEK_THR) > > + sdist = CFQQ_SEEK_THR; > > + > > return cfq_dist_from_last(cfqd, rq) <= sdist; > > } > > > > > This changes also the cfq_should_preempt behaviour, where a large > seek_mean could be meaningful, so I think it is better to add a > boolean parameter to cfq_rq_close, to distinguish whether we are > preempting or looking for queue merges, and make the new code > conditional on merging. can you explain why it's meaningful for cfq_should_preempt()? Unless sdist is very big, for example > 10*seek_mean, the preempt seems not meaningless.
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