Re: [PATCH]cfq-iosched: don't stop async queue with async requests pending

[Corrado Zoccolo <czoccolo@gmail.com>]

On Wed, Jan 13, 2010 at 8:44 AM, Shaohua Li <shaohua.li@intel.com> wrote:
> My SSD speed of direct write is about 80m/s, while I test page writeback,
> the speed can only go to 68m/s. Below patch fixes this.
> It appears we missused cfq_should_idle in cfq_may_dispatch. cfq_should_idle
> means a queue should idle because it's seekless sync queue or it's the last queue,
> which is to maintain service tree time slice. So it doesn't mean the
> last queue is always a sync queue. If the last queue is asyn queue,
> we definitely shouldn't stop dispatch requests because of pending async
> requests.

An other option is that cfq_should_idle returns false for async
queues, since cfq will never idle on them.

Corrado
>
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 918c7fd..8198079 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -2222,7 +2222,8 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>        /*
>         * Drain async requests before we start sync IO
>         */
> -       if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC])
> +       if (cfq_cfqq_sync(cfqq) && cfq_should_idle(cfqd, cfqq)
> +               && cfqd->rq_in_driver[BLK_RW_ASYNC])
>                return false;
>
>        /*
> --
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dott. Corrado Zoccolo                          mailto:czoccolo@gmail.com
PhD - Department of Computer Science - University of Pisa, Italy
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