Re: [PATCH 10/19] io-conroller: Prepare elevator layer for single queue schedulers

Vivek Goyal
2009-06-11T14:43:16Z

On Thu, Jun 11, 2009 at 04:10:55PM +0800, Gui Jianfeng wrote:
> Vivek Goyal wrote:
> ...
> >
> > /*
> > @@ -1296,6 +1302,13 @@ void io_group_chain_link(struct request_queue *q, void *key,
> > iog = io_cgroup_lookup_group(iocg, key);
> > io_group_set_parent(prev, iog);
> > }
> > +
> > + if (unlikely(efqd->only_root_group))
> > + /*
> > + * TODO: Take care of force expiry of existing queue before
> > + * new queue is queued.
> > + */
> > + efqd->only_root_group = 0;
>
> Hi Vivek,
>
> This flag isn't set back when all child groups go away. Am i missing something?
> BTW, why not just determine "only root group" by cgroup itself? Although there might be
> some impact if cgroup is built but no request goes into it. but i think this isn't a big
> deal. How about the following patch?
>

Hi Gui,

Determining if there are any children present or not from cgroup sounds like
a good idea. Just that cost of the operation now has increased. I am not
sure how significant that is. But for the time being we can stick to your
implementation.

One question inline below.

> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
> ---
> block/elevator-fq.c | 21 ++++++++++-----------
> block/elevator-fq.h | 1 -
> 2 files changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/block/elevator-fq.c b/block/elevator-fq.c
> index a516dce..f33155c 100644
> --- a/block/elevator-fq.c
> +++ b/block/elevator-fq.c
> @@ -76,7 +76,6 @@ void elv_del_ioq_busy(struct elevator_queue *e, struct io_queue *ioq,
> void elv_activate_ioq(struct io_queue *ioq, int add_front);
> void elv_deactivate_ioq(struct elv_fq_data *efqd, struct io_queue *ioq,
> int requeue);
> -
> static int bfq_update_next_active(struct io_sched_data *sd)
> {
> struct io_group *iog;
> @@ -1131,6 +1130,14 @@ struct io_cgroup io_root_cgroup = {
> .ioprio_class = IO_DEFAULT_GRP_CLASS,
> };
>
> +static int is_only_root_group(void)
> +{
> + if (list_empty(&io_root_cgroup.css.cgroup->children))
> + return 1;
> +

Do we need some kind of locking here to make sure cgroup->children list is not
being modified?

Thanks
Vivek

> + return 0;
> +}
> +
> void bfq_init_entity(struct io_entity *entity, struct io_group *iog)
> {
> entity->ioprio = entity->new_ioprio;
> @@ -1543,13 +1550,6 @@ void io_group_chain_link(struct request_queue *q, void *key,
> iog = io_cgroup_lookup_group(iocg, key);
> io_group_set_parent(prev, iog);
> }
> -
> - if (unlikely(efqd->only_root_group))
> - /*
> - * TODO: Take care of force expiry of existing queue before
> - * new queue is queued.
> - */
> - efqd->only_root_group = 0;
> }
>
> /**
> @@ -3601,7 +3601,7 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
> * overhead.
> */
>
> - if (efqd->only_root_group && elv_iosched_single_ioq(q->elevator)) {
> + if (is_only_root_group() && elv_iosched_single_ioq(q->elevator)) {
> elv_log_ioq(efqd, ioq, "select: only root group, no expiry");
> goto keep_queue;
> }
> @@ -3872,7 +3872,7 @@ void elv_ioq_completed_request(struct request_queue *q, struct request *rq)
> * unnecessary overhead.
> */
>
> - if (efqd->only_root_group &&
> + if (is_only_root_group() &&
> elv_iosched_single_ioq(q->elevator)) {
> elv_log_ioq(efqd, ioq, "select: only root group,"
> " no expiry");
> @@ -4019,7 +4019,6 @@ int elv_init_fq_data(struct request_queue *q, struct elevator_queue *e)
>
> /* For the time being keep fairness enabled by default */
> efqd->fairness = 1;
> - efqd->only_root_group = 1;
> return 0;
> }
>
> diff --git a/block/elevator-fq.h b/block/elevator-fq.h
> index 1b1fb0b..0939735 100644
> --- a/block/elevator-fq.h
> +++ b/block/elevator-fq.h
> @@ -368,7 +368,6 @@ struct elv_fq_data {
> * queues.
> */
> unsigned int fairness;
> - int only_root_group;
> };
>
> extern int elv_slice_idle;
> --
> 1.5.4.rc3
>
>
>