Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH 2/3] cfq-iosched: Implement a new tunable group_idle | Date | Mon, 19 Jul 2010 14:58:41 -0400 |
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Vivek Goyal <vgoyal@redhat.com> writes:
> o Implement a new tunable group_idle, which allows idling on the group > instead of a cfq queue. Hence one can set slice_idle = 0 and not idle > on the individual queues but idle on the group. This way on fast storage > we can get fairness between groups at the same time overall throughput > improves. > > Signed-off-by: Vivek Goyal <vgoyal@redhat.com> > --- > block/cfq-iosched.c | 60 +++++++++++++++++++++++++++++++++++++++++++++------ > 1 files changed, 53 insertions(+), 7 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index f44064c..b23d7f4 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -30,6 +30,7 @@ static const int cfq_slice_sync = HZ / 10; > static int cfq_slice_async = HZ / 25; > static const int cfq_slice_async_rq = 2; > static int cfq_slice_idle = HZ / 125; > +static int cfq_group_idle = HZ / 125; > static const int cfq_target_latency = HZ * 3/10; /* 300 ms */ > static const int cfq_hist_divisor = 4; > > @@ -198,6 +199,8 @@ struct cfq_group { > struct hlist_node cfqd_node; > atomic_t ref; > #endif > + /* number of requests that are on the dispatch list or inside driver */ > + int dispatched; > }; > > /* > @@ -271,6 +274,7 @@ struct cfq_data { > unsigned int cfq_slice[2]; > unsigned int cfq_slice_async_rq; > unsigned int cfq_slice_idle; > + unsigned int cfq_group_idle; > unsigned int cfq_latency; > unsigned int cfq_group_isolation; > > @@ -1856,6 +1860,9 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq) > BUG_ON(!service_tree); > BUG_ON(!service_tree->count); > > + if (!cfqd->cfq_slice_idle) > + return false; > + > /* We never do for idle class queues. */ > if (prio == IDLE_WORKLOAD) > return false; > @@ -1880,7 +1887,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd) > { > struct cfq_queue *cfqq = cfqd->active_queue; > struct cfq_io_context *cic; > - unsigned long sl; > + unsigned long sl, group_idle = 0; > > /* > * SSD device without seek penalty, disable idling. But only do so > @@ -1896,8 +1903,13 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd) > /* > * idle is disabled, either manually or by past process history > */ > - if (!cfqd->cfq_slice_idle || !cfq_should_idle(cfqd, cfqq)) > - return; > + if (!cfqd->cfq_slice_idle || !cfq_should_idle(cfqd, cfqq)) {
The check for cfqd->cfq_slice_idle is now redundant (as it's done in cfq_should_idle).
> @@ -2215,7 +2236,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) > cfqq = NULL; > goto keep_queue; > } else > - goto expire; > + goto check_group_idle; > } > > /* > @@ -2249,6 +2270,17 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) > goto keep_queue; > } > > + /* > + * If group idle is enabled and there are requests dispatched from > + * this group, wait for requests to complete. > + */ > +check_group_idle: > + if (cfqd->cfq_group_idle && cfqq->cfqg->nr_cfqq == 1 > + && cfqq->cfqg->dispatched) { > + cfqq = NULL; > + goto keep_queue; > + }
I really wish we could roll all of this logic into cfq_should_idle.
> @@ -3420,7 +3453,10 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq) > * the queue. > */ > if (cfq_should_wait_busy(cfqd, cfqq)) { > - cfqq->slice_end = jiffies + cfqd->cfq_slice_idle; > + unsigned long extend_sl = cfqd->cfq_slice_idle; > + if (!cfqd->cfq_slice_idle) > + extend_sl = cfqd->cfq_group_idle; > + cfqq->slice_end = jiffies + extend_sl;
So, if slice_idle and group_idle are both set, slice_idle trumps group_idle? Did you give that case any thought? If it doesn't make sense to configure both, then we should probably make sure they can't both be set.
Cheers, Jeff
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