From mboxrd@z Thu Jan  1 00:00:00 1970
From: hch@lst.de (Christoph Hellwig)
Date: Thu, 13 Dec 2018 16:52:35 +0100
Subject: [PATCH v2 6/6] nvme-multipath: disable polling for underlying
 namespace request queue
In-Reply-To: <4f3f213e-9042-5963-d47d-0ee501bf94fa@grimberg.me>
References: <20181213063819.13614-1-sagi@grimberg.me>
 <20181213063819.13614-7-sagi@grimberg.me> <20181213083157.GD869@lst.de>
 <4f3f213e-9042-5963-d47d-0ee501bf94fa@grimberg.me>
Message-ID: <20181213155235.GA10566@lst.de>

On Thu, Dec 13, 2018@07:49:42AM -0800, Sagi Grimberg wrote:
>
>> +	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
>> +		bio->bi_opf &= ~REQ_HIPRI;
>> +
>
> Maybe we can simply check (q->queue_flags & (1 << QUEUE_FLAG_POLL)) and
> avoid the extra atomic operation in the host path?
>
> Would it make sense?

test_bit is not usually implemented as an atomic operation.

Take a look at e.g.

arch/x86/include/asm/bitops.h:constant_test_bit()