From: Jens Axboe <axboe@kernel.dk>
To: "jianchao.wang" <jianchao.w.wang@oracle.com>,
Ming Lei <ming.lei@redhat.com>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued
Date: Tue, 12 Sep 2017 21:54:06 -0600 [thread overview]
Message-ID: <17775b50-1bf2-26d2-c371-2eb349be85d6@kernel.dk> (raw)
In-Reply-To: <aebfc622-6d7d-0d07-5a13-8dae06a49bb7@oracle.com>
On 09/12/2017 09:39 PM, jianchao.wang wrote:
>> Exactly, and especially the readability is the key element here. It's
>> just not worth it to try and be too clever, especially not for
>> something like this. When you read the above, you immediately know
>> what the code does without needing a comment. That's not true for the
>> other construct. You both have to read other parts of the function
>> to figure out what it does, AND read the entire function to ensure it
>> always does the right thing. Fragile.
>
> Thanks for your comments , jens and ming. I'm really appreciative of
> that. About the fragility, do you mean the possibility that may
> release the tag of the next rq which has a driver tag itself (maybe a
> flush) ?
I mean that if you do:
if (!list_empty(list))
blk_mq_put_driver_tag(nxt);
it's fragile code in the sense that changes elsewhere in the function
are harder to validate and/or can impact the functionality of that
simple if and tag put.
The actual release must always be safe, of course.
--
Jens Axboe
next prev parent reply other threads:[~2017-09-13 3:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-12 17:14 [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued Jianchao Wang
2017-09-12 10:23 ` Ming Lei
2017-09-13 1:01 ` jianchao.wang
2017-09-13 1:24 ` Ming Lei
2017-09-13 1:39 ` jianchao.wang
2017-09-13 1:52 ` Ming Lei
2017-09-13 2:23 ` Jens Axboe
2017-09-13 2:42 ` jianchao.wang
2017-09-13 2:45 ` Jens Axboe
2017-09-13 3:39 ` jianchao.wang
2017-09-13 3:54 ` Jens Axboe [this message]
2017-09-13 3:59 ` jianchao.wang
2017-09-13 3:50 ` Ming Lei
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