linux-kernel - Re: [PATCH BUGFIX V2] block, bfq: fix operator in BFQQ_TOTALLY

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Message-Id: <D9A203CB-DDA2-4C67-A20C-A3CA7354E3FB@linaro.org>
Date:   Mon, 24 Jun 2019 21:18:17 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block <linux-block@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>, linus.walleij@...aro.org,
        bfq-iosched@...glegroups.com, oleksandr@...alenko.name
Subject: Re: [PATCH BUGFIX V2] block, bfq: fix operator in BFQQ_TOTALLY_SEEKY



> Il giorno 24 giu 2019, alle ore 18:12, Jens Axboe <axboe@...nel.dk> ha scritto:
> 
> On 6/22/19 2:44 PM, Paolo Valente wrote:
>> By mistake, there is a '&' instead of a '==' in the definition of the
>> macro BFQQ_TOTALLY_SEEKY. This commit replaces the wrong operator with
>> the correct one.
> 
> A bit worrying that this wasn't caught in testing, as it would have
> resulted in _any_ queue being positive for totally seeky?
> 

Fortunately there's a somewhat reassuring explanation.  The commit
introducing this macro prevented seeky queues from being considered
soft real-time.  And, to be more selective, it actually filtered out
only totally seeky queues, i.e., queues whose last I/O requests are
*all* random.  With this error, any seeky queue was considered totally
seeky.  This the broke (only) selectivity.

> Anyway, applied.
> 

Thanks,
Paolo

> -- 
> Jens Axboe
>