Messages in this thread |  | | | Date | Mon, 09 Nov 2009 15:41:07 +0800 | | From | Gui Jianfeng <> | | Subject | Re: [PATCH 15/20] blkio: Take care of preemptions across groups |
Vivek Goyal wrote: > On Fri, Nov 06, 2009 at 03:55:58PM +0800, Gui Jianfeng wrote: >> Vivek Goyal wrote: >>> o Additional preemption checks for groups where we travel up the hierarchy >>> and see if one queue should preempt other or not. >>> >>> o Also prevents preemption across groups in some cases to provide isolation >>> between groups. >>> >>> Signed-off-by: Vivek Goyal <vgoyal@redhat.com> >>> --- >>> block/cfq-iosched.c | 33 +++++++++++++++++++++++++++++++++ >>> 1 files changed, 33 insertions(+), 0 deletions(-) >>> >>> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c >>> index 87b1799..98dbead 100644 >>> --- a/block/cfq-iosched.c >>> +++ b/block/cfq-iosched.c >>> @@ -2636,6 +2636,36 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq, >>> } >>> } >>> >>> +static bool cfq_should_preempt_group(struct cfq_data *cfqd, >>> + struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) >>> +{ >>> + struct cfq_entity *cfqe = &cfqq->entity; >>> + struct cfq_entity *new_cfqe = &new_cfqq->entity; >>> + >>> + if (cfqq_to_cfqg(cfqq) != &cfqd->root_group) >>> + cfqe = parent_entity(&cfqq->entity); >>> + >>> + if (cfqq_to_cfqg(new_cfqq) != &cfqd->root_group) >>> + new_cfqe = parent_entity(&new_cfqq->entity); >>> + >>> + /* >>> + * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice. >>> + */ >>> + >>> + if (new_cfqe->ioprio_class == IOPRIO_CLASS_RT >>> + && cfqe->ioprio_class != IOPRIO_CLASS_RT) >>> + return true; >>> + /* >>> + * Allow an BE request to pre-empt an ongoing IDLE clas timeslice. >>> + */ >>> + >>> + if (new_cfqe->ioprio_class == IOPRIO_CLASS_BE >>> + && cfqe->ioprio_class == IOPRIO_CLASS_IDLE) >>> + return true; >>> + >>> + return false; >>> +} >>> + >>> /* >>> * Check if new_cfqq should preempt the currently active queue. Return 0 for >>> * no or if we aren't sure, a 1 will cause a preempt. >>> @@ -2666,6 +2696,9 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, >>> if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq)) >>> return true; >>> >>> + if (cfqq_to_cfqg(new_cfqq) != cfqq_to_cfqg(cfqq)) >>> + return cfq_should_preempt_group(cfqd, cfqq, new_cfqq); >>> + >> Vivek, why not put cfq_should_preempt_group() at the beginning of cfq_should_preempt() >> to prevent preemption across groups? > > Hi Gui, > > Currently the checks before the group check were not hurting much, that's > why. > > The only contentious check will be if a sync IO in one group should > preempt the async IO in other group or not.
In my opinion, sync IO should not preempt async one in other group from the fairness point of view.
Thanks Gui
|  |