Messages in this thread | | | Date | Mon, 28 Dec 2009 10:40:12 +0100 | Subject | Re: [PATCH]cfq-iosched: don't take requests with long distence as close | From | Corrado Zoccolo <> |
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On Mon, Dec 28, 2009 at 10:28 AM, Shaohua Li <shaohua.li@intel.com> wrote: > On Mon, Dec 28, 2009 at 05:11:25PM +0800, Corrado Zoccolo wrote: >> Hi Shaohua, >> On Mon, Dec 28, 2009 at 9:46 AM, Shaohua Li <shaohua.li@intel.com> wrote: >> > 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. >> >> Disk access time is a complex function, but for rotational disks it is >> 'sort of' increasing with the amplitude of the seek. So, if you have a >> new request that is within the mean seek distance (even if it is >> larger than our constant), it is good to chose this request instead of >> waiting for an other one from the active queue (this behaviour is the >> same exhibited by AS, so we need a good reason to change). > I have no good reason, but just thought it's a little strange. > If other ioscheds take the same way, let's stick. > > > seek_mean could be very big sometimes, using it as close criteria is meaningless > as this doen't improve any performance. So if it's big, let's fallback to > default value. > > Signed-off-by: Shaohua Li<shaohua.li@intel.com> Reviewed-by: Corrado Zoccolo <czoccolo@gmail.com> > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index e2f8046..e80bd47 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -1675,13 +1675,17 @@ static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd, > #define CFQQ_SEEKY(cfqq) ((cfqq)->seek_mean > CFQQ_SEEK_THR) > > static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq, > - struct request *rq) > + struct request *rq, bool for_preempt) > { > sector_t sdist = cfqq->seek_mean; > > if (!sample_valid(cfqq->seek_samples)) > sdist = CFQQ_SEEK_THR; > > + /* if seek_mean is big, using it as close criteria is meaningless */ > + if (sdist > CFQQ_SEEK_THR && !for_preempt) > + sdist = CFQQ_SEEK_THR; > + > return cfq_dist_from_last(cfqd, rq) <= sdist; > } > > @@ -1709,7 +1713,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd, > * will contain the closest sector. > */ > __cfqq = rb_entry(parent, struct cfq_queue, p_node); > - if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq)) > + if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false)) > return __cfqq; > > if (blk_rq_pos(__cfqq->next_rq) < sector) > @@ -1720,7 +1724,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd, > return NULL; > > __cfqq = rb_entry(node, struct cfq_queue, p_node); > - if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq)) > + if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq, false)) > return __cfqq; > > return NULL; > @@ -3143,7 +3147,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, > * if this request is as-good as one we would expect from the > * current cfqq, let it preempt > */ > - if (cfq_rq_close(cfqd, cfqq, rq)) > + if (cfq_rq_close(cfqd, cfqq, rq, true)) > return true; > > return false; > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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