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From: hch@lst.de (Christoph Hellwig)
Subject: [PATCH 7/8] nvme/pci: Remove volatile from cqe
Date: Wed, 27 Mar 2019 14:55:48 +0100	[thread overview]
Message-ID: <20190327135548.GE25849@lst.de> (raw)
In-Reply-To: <ad2add1c-efa6-c446-9685-6ea4ce7c2c45@grimberg.me>

On Mon, Mar 11, 2019@04:56:14PM -0700, Sagi Grimberg wrote:
>
>>> The cqe isn't volatile once we confirm the phase bit. Remove the volatile
>>> keyword and let the compiler optimize out an unnecessary additional read
>>> to the command id.
>>
>> Hmm.  I've never been happy about how we used volatile to start with,
>> but I'm not sure more casts sort out this problem.
>>
>> Wouldn't the right fix be to drop the volatile entirely and force
>> a strong barrier before first reading the phase bit?
>
> Is there a fundamental difference efficiency-wise?

I'm not sure.  The latter is just more our usual Linux style.

  reply	other threads:[~2019-03-27 13:55 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-08 17:43 [PATCH 1/8] nvme/pci: Use a flag for polled queues Keith Busch
2019-03-08 17:43 ` [PATCH 2/8] nvme/pci: Don't poll polled queues in timeout Keith Busch
2019-03-11 18:25   ` Christoph Hellwig
2019-03-11 23:33   ` Sagi Grimberg
2019-03-08 17:43 ` [PATCH 3/8] nvme/pci: Remove tag check in nvme_process_cq Keith Busch
2019-03-11 18:26   ` Christoph Hellwig
2019-03-11 23:35   ` Sagi Grimberg
2019-03-08 17:43 ` [PATCH 4/8] nvme/pci: Remove last_cq_seen Keith Busch
2019-03-11 18:28   ` Christoph Hellwig
2019-03-11 23:40     ` Sagi Grimberg
2019-03-27 13:55       ` Christoph Hellwig
2019-03-08 17:43 ` [PATCH 5/8] nvme/pci: Remove last_sq_tail Keith Busch
2019-03-11 18:31   ` Christoph Hellwig
2019-03-11 19:21     ` Keith Busch
2019-03-11 23:53       ` Sagi Grimberg
2019-03-08 17:43 ` [PATCH 6/8] nvme/pci: Remove q_dmadev from nvme_queue Keith Busch
2019-03-11 18:31   ` Christoph Hellwig
2019-03-11 23:54   ` Sagi Grimberg
2019-03-27 13:53   ` Christoph Hellwig
2019-03-08 17:43 ` [PATCH 7/8] nvme/pci: Remove volatile from cqe Keith Busch
2019-03-11 18:33   ` Christoph Hellwig
2019-03-11 23:56     ` Sagi Grimberg
2019-03-27 13:55       ` Christoph Hellwig [this message]
2019-03-08 17:43 ` [PATCH 8/8] nvme/pci: Remove unused nvme_iod member Keith Busch
2019-03-11 18:33   ` Christoph Hellwig
2019-03-11 23:56   ` Sagi Grimberg
2019-03-27 13:53   ` Christoph Hellwig
2019-03-11 18:25 ` [PATCH 1/8] nvme/pci: Use a flag for polled queues Christoph Hellwig
2019-03-11 23:31 ` Sagi Grimberg
2019-03-27 13:53 ` Christoph Hellwig

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