linux-kernel - Re: [PATCH V10 1/8] block, bfq: split sync bfq

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Message-Id: <918DD21A-0099-4EF9-955B-CAED2A3F8947@linaro.org>
Date:   Wed, 21 Dec 2022 11:30:35 +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 V10 1/8] block, bfq: split sync bfq_queues on a
 per-actuator basis



> Il giorno 21 dic 2022, alle ore 11:13, Paolo Valente <paolo.valente@...aro.org> ha scritto:
> 
> 
> 
>> Il giorno 21 dic 2022, alle ore 01:50, Damien Le Moal <damien.lemoal@...nsource.wdc.com> ha scritto:
>> 
>> On 2022/12/20 22:10, Paolo Valente wrote:
>>>>> -	/*
>>>>> -	 * Does queue (or any parent entity) exceed number of requests that
>>>>> -	 * should be available to it? Heavily limit depth so that it cannot
>>>>> -	 * consume more available requests and thus starve other entities.
>>>>> -	 */
>>>>> -	if (bfqq && bfqq_request_over_limit(bfqq, limit))
>>>>> -		depth = 1;
>>>>> +	for (act_idx = 0; act_idx < bfqd->num_actuators; act_idx++) {
>>>>> +		struct bfq_queue *bfqq =
>>>>> +			bic ? bic_to_bfqq(bic, op_is_sync(opf), act_idx) : NULL;
>>>> 
>>>> Commented already: why not add a "if (!bfqq) return NULL;" in
>>>> bic_to_bfqq() ?
>>> 
>>> You have probably missed my reply on this.  The problem is that your
>>> proposal would improve code (only) here, but it would entail the above
>>> control for all the other invocations, for which it is useless :(
>> 
>> But then you have *a lot* of "if (bfqd)" tests that are useless elsewhere since
>> bic_to_bfqq() never returns NULL.
>> 
> 
> I'm probably misunderstanding your point, sorry.  Could you point me
> to one of the places where there is the useless control that would go
> away if we add your proposed control inside bic_to_bfqq?

You had already done that in a following email, sorry.  I have replied
to that email of yours.

Thanks,
Paolo