From: John Garry <john.garry@huawei.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
QiuLaibin <qiulaibin@huawei.com>
Cc: <axboe@kernel.dk>, <ming.lei@redhat.com>,
<martin.petersen@oracle.com>, <hare@suse.de>,
<johannes.thumshirn@wdc.com>, <bvanassche@acm.org>,
<linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -next v4] blk-mq: fix tag_get wait task can't be awakened
Date: Wed, 12 Jan 2022 12:51:13 +0000 [thread overview]
Message-ID: <3d386998-d810-5036-a87e-50aba9f56639@huawei.com> (raw)
In-Reply-To: <Yd7J4XbkdIm52bVw@smile.fi.intel.com>
On 12/01/2022 12:30, Andy Shevchenko wrote:
>>>> + if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) ||
>>>> + test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags)) {
>>> Whoever wrote this code did too much defensive programming, because the first
>>> conditional doesn't make much sense here. Am I right?
>>>
>> I think because this judgement is in the general IO process, there are also
>> some performance considerations here.
> I didn't buy this. Is there any better argument why you need redundant
> test_bit() call?
>
I think that the idea is that test_bit() is fast and test_and_set_bit()
is slow; as such, if we generally expect the bit to be set, then there
is no need to do the slower test_and_set_bit() always.
next prev parent reply other threads:[~2022-01-12 12:51 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-11 14:02 [PATCH -next v4] blk-mq: fix tag_get wait task can't be awakened Laibin Qiu
2022-01-11 14:15 ` Andy Shevchenko
2022-01-12 4:18 ` QiuLaibin
2022-01-12 12:30 ` Andy Shevchenko
2022-01-12 12:51 ` John Garry [this message]
2022-01-12 14:38 ` Andy Shevchenko
2022-01-12 15:37 ` Jens Axboe
2022-01-12 16:29 ` Andy Shevchenko
2022-01-12 16:38 ` Jens Axboe
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