linux-kernel - Re: [PATCH -next v6 3/3] block, bfq: do not idle if only one group is activated

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Message-Id: <27B0AE8B-C134-4BA1-B84F-39C659CB2B10@linaro.org>
Date:   Sat, 28 May 2022 10:30:34 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     Jan Kara <jack@...e.cz>, tj@...nel.org, axboe@...nel.dk,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH -next v6 3/3] block, bfq: do not idle if only one group is
 activated



> Il giorno 23 mag 2022, alle ore 15:18, Yu Kuai <yukuai3@...wei.com> ha scritto:
> 
> Now that root group is counted into 'num_groups_with_busy_queues',
> 'num_groups_with_busy_queues > 0' is always true in
> bfq_asymmetric_scenario(). Thus change the condition to '> 1'.
> 
> On the other hand, this change can enable concurrent sync io if only
> one group is activated.

This is ok.  Yet, if the mistakes I found in the other two patches are
actual errors, I wonder how these changes made it to pass your tests.

Thanks,
Paolo

> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> ---
> block/bfq-iosched.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 609b4e894684..142e1ca4600f 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -812,7 +812,7 @@ bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
>  * much easier to maintain the needed state:
>  * 1) all active queues have the same weight,
>  * 2) all active queues belong to the same I/O-priority class,
> - * 3) there are no active groups.
> + * 3) there are one active group at most.
>  * In particular, the last condition is always true if hierarchical
>  * support or the cgroups interface are not enabled, thus no state
>  * needs to be maintained in this case.
> @@ -844,7 +844,7 @@ static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
> 
> 	return varied_queue_weights || multiple_classes_busy
> #ifdef CONFIG_BFQ_GROUP_IOSCHED
> -	       || bfqd->num_groups_with_busy_queues > 0
> +	       || bfqd->num_groups_with_busy_queues > 1
> #endif
> 		;
> }
> -- 
> 2.31.1
>