Messages in this thread | | | Subject | Re: [RFC PATCH] cfq: Give a chance for arming slice idle timer in case of group_idle | From | Ritesh Harjani <> | Date | Fri, 11 Aug 2017 10:45:08 +0530 |
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Hi Jens,
Could you please take a look at below patch and the issue it is trying to solve. Please let us know your thoughts on the below problem and the patch.
Regards Ritesh
On 8/9/2017 6:28 PM, Ritesh Harjani wrote: > In below scenario blkio cgroup does not work as per their assigned > weights :- > 1. When the underlying device is nonrotational with a single HW queue > with depth of >= CFQ_HW_QUEUE_MIN > 2. When the use case is forming two blkio cgroups cg1(weight 1000) & > cg2(wight 100) and two processes(file1 and file2) doing sync IO in > their respective blkio cgroups. > > For above usecase result of fio (without this patch):- > file1: (groupid=0, jobs=1): err= 0: pid=685: Thu Jan 1 19:41:49 1970 > write: IOPS=1315, BW=41.1MiB/s (43.1MB/s)(1024MiB/24906msec) > <...> > file2: (groupid=0, jobs=1): err= 0: pid=686: Thu Jan 1 19:41:49 1970 > write: IOPS=1295, BW=40.5MiB/s (42.5MB/s)(1024MiB/25293msec) > <...> > // both the process BW is equal even though they belong to diff. > cgroups with weight of 1000(cg1) and 100(cg2) > > In above case (for non rotational NCQ devices), > as soon as the request from cg1 is completed and even > though it is provided with higher set_slice=10, because of CFQ > algorithm when the driver tries to fetch the request, CFQ expires > this group without providing any idle time nor weight priority > and schedules another cfq group (in this case cg2). > And thus both cfq groups(cg1 & cg2) keep alternating to get the > disk time and hence loses the cgroup weight based scheduling. > > Below patch gives a chance to cfq algorithm (cfq_arm_slice_timer) > to arm the slice timer in case group_idle is enabled. > In case if group_idle is also not required (including for nonrotational > NCQ drives), we need to explicitly set group_idle = 0 from sysfs for > such cases. > > With this patch result of fio(for above usecase) :- > file1: (groupid=0, jobs=1): err= 0: pid=690: Thu Jan 1 00:06:08 1970 > write: IOPS=1706, BW=53.3MiB/s (55.9MB/s)(1024MiB/19197msec) > <..> > file2: (groupid=0, jobs=1): err= 0: pid=691: Thu Jan 1 00:06:08 1970 > write: IOPS=1043, BW=32.6MiB/s (34.2MB/s)(1024MiB/31401msec) > <..> > // In this processes BW is as per their respective cgroups weight. > > Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org> > --- > block/cfq-iosched.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 0fb78fb..15cad96 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -2934,7 +2934,8 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd) > * for devices that support queuing, otherwise we still have a problem > * with sync vs async workloads. > */ > - if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag) > + if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag && > + !cfqd->cfq_group_idle) > return; > > WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list)); >
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