Messages in this thread | | | Date | Wed, 13 Jan 2010 22:30:52 +0100 | Subject | Re: [PATCH]cfq-iosched: don't stop async queue with async requests pending | From | Corrado Zoccolo <> |
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On Wed, Jan 13, 2010 at 12:10 PM, Vivek Goyal <vgoyal@redhat.com> wrote: > On Wed, Jan 13, 2010 at 03:44:42PM +0800, Shaohua Li wrote: >> My SSD speed of direct write is about 80m/s, while I test page writeback, >> the speed can only go to 68m/s. Below patch fixes this. >> It appears we missused cfq_should_idle in cfq_may_dispatch. cfq_should_idle >> means a queue should idle because it's seekless sync queue or it's the last queue, >> which is to maintain service tree time slice. So it doesn't mean the >> last queue is always a sync queue. If the last queue is asyn queue, >> we definitely shouldn't stop dispatch requests because of pending async >> requests. >> >> Signed-off-by: Shaohua Li <shaohua.li@intel.com> >> >> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c >> index 918c7fd..8198079 100644 >> --- a/block/cfq-iosched.c >> +++ b/block/cfq-iosched.c >> @@ -2222,7 +2222,8 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq) >> /* >> * Drain async requests before we start sync IO >> */ >> - if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC]) >> + if (cfq_cfqq_sync(cfqq) && cfq_should_idle(cfqd, cfqq) >> + && cfqd->rq_in_driver[BLK_RW_ASYNC]) >> return false; > > So are we driving queue depth as 1 when pure buffered writes are going on? > Because in that case service_tree->count=1 and cfq_should_idle() will > return 1 and looks like we will not dispatch next write till previous > write is over?
Yes, it seems so. It has to be fixed.
> > A general question. Why do we need to drain async requests before we start > sync IO? How does that help? > > A related question, even if we have to do that, why do we check for > cfq_should_idle()? Why can't we just do following. > > if (cfq_cfqq_sync(cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC]) > This would wait also for seeky queues. I think we drain to avoid disrupting a sync stream with far writes, but it is not needed when the queues are already seeky.
Thanks, Corrado > Thanks > Vivek > -- > 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/ > -- 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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