Messages in this thread | | | Date | Thu, 18 Mar 2010 17:55:16 +0100 | Subject | Re: [RFC]cfq-iosched: fix a kbuild regression | From | Corrado Zoccolo <> |
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On Thu, Mar 18, 2010 at 2:05 AM, Shaohua Li <shaohua.li@intel.com> wrote: > On Thu, Mar 18, 2010 at 02:24:10AM +0800, Corrado Zoccolo wrote: >> On Wed, Mar 17, 2010 at 2:30 PM, Jens Axboe <jens.axboe@oracle.com> wrote: >> > On Tue, Mar 16 2010, Shaohua Li wrote: >> >> Alex Shi reported a kbuild regression which is about 10% performance lost. >> >> He bisected to this commit: 3dde36ddea3e07dd025c4c1ba47edec91606fec0. >> >> The reason is cfqq_close() can't find close cooperator. If we store the seek >> >> distance to the value before the commit like below, the regression fully goes >> >> away. If this is too invasive, just changing the cfq_rq_close() for the >> >> !for_preempt is ok too. >> > >> > Corrado, any objections to widening the seek threshold? >> >> The previous seek threshold value was meant to be compared with the >> average seek distance, so it was large to account for variations. >> Since we handle the variations differently, we should have a smaller >> value now (the 100 * 8 was the result of a benchmark run on several >> disks). > Our test doesn't find any issue with the seek threshold so far, so it proberly > is ok. > >> I agreee, though, that for merging queues, it is now too small, so we >> should have two thresholds, the current one used to determine if a >> request causes a seek, and an other to be used inside cfq_close (with >> the older value, regardless of for_preempt). > That makes sense. Updated patch. > > > Alex Shi reported a kbuild regression which is about 10% performance lost. > He bisected to this commit: 3dde36ddea3e07dd025c4c1ba47edec91606fec0. > The reason is cfqq_close() can't find close cooperator. Restoring > cfq_rq_close()'s threshold to original value makes the regression go away. > > Since for_preempt parameter isn't used anymore, this patch deletes it. > > Reported-by: Alex Shi <alex.shi@intel.com> > Signed-off-by: Shaohua Li <shaohua.li@intel.com> Acked-by: Corrado Zoccolo <czoccolo@gmail.com> > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index dee9d93..8d5a2f2 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -47,6 +47,7 @@ static const int cfq_hist_divisor = 4; > #define CFQ_SERVICE_SHIFT 12 > > #define CFQQ_SEEK_THR (sector_t)(8 * 100) > +#define CFQQ_CLOSE_THR (sector_t)(8 * 1024) > #define CFQQ_SECT_THR_NONROT (sector_t)(2 * 32) > #define CFQQ_SEEKY(cfqq) (hweight32(cfqq->seek_history) > 32/8) > > @@ -1660,9 +1661,9 @@ static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd, > } > > static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq, > - struct request *rq, bool for_preempt) > + struct request *rq) > { > - return cfq_dist_from_last(cfqd, rq) <= CFQQ_SEEK_THR; > + return cfq_dist_from_last(cfqd, rq) <= CFQQ_CLOSE_THR; > } > > static struct cfq_queue *cfqq_close(struct cfq_data *cfqd, > @@ -1689,7 +1690,7 @@ 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, false)) > + if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq)) > return __cfqq; > > if (blk_rq_pos(__cfqq->next_rq) < sector) > @@ -1700,7 +1701,7 @@ 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, false)) > + if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq)) > return __cfqq; > > return NULL; > @@ -3103,7 +3104,7 @@ 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, true)) > + if (cfq_rq_close(cfqd, cfqq, rq)) > 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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