linux-kernel - Re: [PATCH V11 1/8] block, bfq: split sync bfq

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Date:   Thu, 22 Dec 2022 15:37:28 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arie van der Hoeven <arie.vanderhoeven@...gate.com>,
        Rory Chen <rory.c.chen@...gate.com>,
        Glen Valante <glen.valante@...aro.org>,
        Gabriele Felici <felicigb@...il.com>,
        Carmine Zaccagnino <carmine@...minezacc.com>
Subject: Re: [PATCH V11 1/8] block, bfq: split sync bfq_queues on a
 per-actuator basis



> Il giorno 21 dic 2022, alle ore 13:27, Damien Le Moal <damien.lemoal@...nsource.wdc.com> ha scritto:
> 
> On 2022/12/21 19:27, Paolo Valente wrote:
>> 
>> 
>>> Il giorno 21 dic 2022, alle ore 01:46, Damien Le Moal <damien.lemoal@...nsource.wdc.com> ha scritto:
>>> 
>>> 
>>> [...]
>>> 
>>>> -static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
>>>> +static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync,
>>>> +			      unsigned int actuator_idx)
>>>> {
>>>> -	struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
>>>> +	struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync, actuator_idx);
>>>> 	struct bfq_data *bfqd;
>>>> 
>>>> 	if (bfqq)
>>> 
>>> With your current bic_to_bfqq() implementation, you will *never* get NULL as a
>>> return value.
>> 
>> I'm afraid this is not true.  A bic is associated with a sync and an
>> async queue, or with both.  So, in the hunk above, bic_to_bfqq returns
>> NULL if:
>> - either the bic is associated with a sync queue, but is_sync happens to be false;
>> - or the bic is associate with an async queue, but is_sync happens to be true.
>> 
>> Of course, with these patches, the associations move from "with a
>> sync/async queue" to "with a set of sync/async queues, one per
>> actuator".
> 
> My bad... The bic->bfqq[][actuator_idx] is an array of pointers... I was reading
> it as "&bic->bfqq[1][actuator_idx]". So please ignore. Apologies for the noise.
> 

Great, then the last bit of action for me is to turn the offending
conditional operation into an if statement.  I'm going to do that and
send a V12 with this change, and with only this first patch still
needing your approval.

Thanks,
Paolo