linux-kernel - Re: [PATCH BUGFIX] block, bfq: update wr_busy

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Date:   Mon, 19 Jun 2017 13:42:44 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        Linux-Kernal <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH BUGFIX] block, bfq: update wr_busy_queues if needed on a queue split


> Il giorno 19 giu 2017, alle ore 09:38, kbuild test robot <lkp@...el.com> ha scritto:
> 
> Hi Paolo,
> 
> [auto build test WARNING on v4.12-rc5]
> [also build test WARNING on next-20170616]
> [cannot apply to block/for-next]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Paolo-Valente/block-bfq-update-wr_busy_queues-if-needed-on-a-queue-split/20170619-145003
> config: i386-randconfig-x000-201725 (attached as .config)
> compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
> reproduce:
>        # save the attached .config to linux build tree
>        make ARCH=i386 
> 
> Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
> 
> All warnings (new ones prefixed by >>):
> 
>   block/bfq-iosched.c: In function 'bfq_get_rq_private':
>>> block/bfq-iosched.c:770:10: warning: 'old_wr_coeff' may be used uninitialized in this function [-Wmaybe-uninitialized]
>     else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
>             ^
>   block/bfq-iosched.c:731:15: note: 'old_wr_coeff' was declared here
>     unsigned int old_wr_coeff;
>                  ^~~~~~~~~~~~
> 

I'm sending a V2, (probably imperceptibly) slower on average, but not
confusing the compiler.

Thanks,
Paolo

> vim +/old_wr_coeff +770 block/bfq-iosched.c
> 
>   754		    time_is_before_jiffies(bfqq->last_wr_start_finish +
>   755					   bfqq->wr_cur_max_time))) {
>   756			bfq_log_bfqq(bfqq->bfqd, bfqq,
>   757			    "resume state: switching off wr");
>   758	
>   759			bfqq->wr_coeff = 1;
>   760		}
>   761	
>   762		/* make sure weight will be updated, however we got here */
>   763		bfqq->entity.prio_changed = 1;
>   764	
>   765		if (likely(!busy))
>   766			return;
>   767	
>   768		if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
>   769			bfqd->wr_busy_queues++;
>> 770		else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
>   771			bfqd->wr_busy_queues--;
>   772	}
>   773	
>   774	static int bfqq_process_refs(struct bfq_queue *bfqq)
>   775	{
>   776		return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
>   777	}
>   778	
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
> <.config.gz>