linux-kernel - Re: [PATCH RFC 3/3] lib/sbitmap: fix shallow

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Message-ID: <3e401555-e971-44c2-b9a4-5c746baaca8a@acm.org>
Date: Mon, 9 Dec 2024 10:11:54 -0800
From: Bart Van Assche <bvanassche@....org>
To: Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk,
 akpm@...ux-foundation.org, yang.yang@...o.com, ming.lei@...hat.com,
 yukuai3@...wei.com, osandov@...com, paolo.valente@...aro.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH RFC 3/3] lib/sbitmap: fix shallow_depth tag allocation

On 12/9/24 7:55 PM, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> Currently, shallow_depth is used by bfq, kyber and mq-deadline, they both
> pass in the value for the whole sbitmap, while sbitmap treate the value
> for just one word. Which means, shallow_depth never work as expected,
> and there really is no such functional tests to covert it.

treate -> treats

The above text is incorrect. I have verified that shallow_depth 
restricts the queue depth of asynchronous requests for mq-deadline if it
is reduced from its default value. The function dd_word_to_depth() in
mq-deadline converts the value written into the sysfs attribute into a
value that is appropriate for the sbitmap implementation.

That being said, it seems like a good idea to me to modify how the
sbitmap code interprets 'shallow_depth'.

Thanks,

Bart.