Messages in this thread Patch in this message | | | Date | Thu, 23 Jun 2011 16:34:59 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH] cfq-iosched: allow groups preemption for sync-noidle workloads |
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On Thu, Jun 23, 2011 at 08:21:59PM +0400, Konstantin Khlebnikov wrote: > commit v2.6.32-102-g8682e1f "blkio: Provide some isolation between groups" break > fast switching between task and journal-thread for very common write-fsync workload. > cfq wait idle slice at each cfqq switch, if this task is from non-root blkio cgroup. > > This patch move idling sync-noidle preempting check little bit upwards and update > new service_tree->count check for case with two different groups. > I do not quite understand what means these check for new_cfqq, but now it even works. > > Without patch I got 49 iops and with this patch 798, for this trivial fio script: > > [write-fsync] > cgroup=test > cgroup_weight=1000 > rw=write > fsync=1 > size=100m > runtime=10s
What kind of storage and filesystem you are using? I tried this on a SATA disk and I really don't get good throughput. With deadline scheduler I get aggrb=103KB/s.
I think with fsync we are generating so many FLUSH requests that it really slows down fsync.
Even if I use CFQ with and without cgroups, I get following.
CFQ, without cgroup ------------------ aggrb=100KB/s
CFQ with cgroup -------------- aggrb=94KB/s
So with FLUSH requests, not much difference in throughput for this workload.
I guess you must be running with barriers off or something like that.
Thanks Vivek
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org> > --- > block/cfq-iosched.c | 14 +++++++------- > 1 files changed, 7 insertions(+), 7 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 3c7b537..c71533e 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -3318,19 +3318,19 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, > if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq)) > return true; > > - if (new_cfqq->cfqg != cfqq->cfqg) > - return false; > - > - if (cfq_slice_used(cfqq)) > - return true; > - > /* Allow preemption only if we are idling on sync-noidle tree */ > if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD && > cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD && > - new_cfqq->service_tree->count == 2 && > + new_cfqq->service_tree->count == 1+(new_cfqq->cfqg == cfqq->cfqg) && > RB_EMPTY_ROOT(&cfqq->sort_list)) > return true; > > + if (new_cfqq->cfqg != cfqq->cfqg) > + return false; > + > + if (cfq_slice_used(cfqq)) > + return true; > + > /* > * So both queues are sync. Let the new request get disk time if > * it's a metadata request and the current queue is doing regular IO.
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