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SubjectRe: [PATCH 15/20] blkio: Take care of preemptions across groups
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?

--
Regards
Gui Jianfeng



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