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Date:   Mon, 13 May 2019 16:54:15 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Mario.Limonciello@dell.com
Cc:     hch@lst.de, keith.busch@intel.com, sagi@grimberg.me,
        linux-nvme@lists.infradead.org, rafael@kernel.org,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        kai.heng.feng@canonical.com
Subject: Re: [PATCH] nvme/pci: Use host managed power state for suspend
Message-ID: <20190513145415.GA25774@lst.de>
References: <20190510212937.11661-1-keith.busch@intel.com> <0080aaff18e5445dabca509d4113eca8@AUSX13MPC105.AMER.DELL.COM> <955722d8fc16425dbba0698c4806f8fd@AUSX13MPC105.AMER.DELL.COM> <20190513143741.GA25500@lst.de> <b12ff66f8c224e4199ff1b90ed6bc393@AUSX13MPC105.AMER.DELL.COM>
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On Mon, May 13, 2019 at 02:43:43PM +0000, Mario.Limonciello@dell.com wrote:
> Well I've got a thought, quoting the NVME spec:
> "After a successful completion of a Set Features command for this feature, the controller shall be in the
> Power State specified. If enabled, autonomous power state transitions continue to occur from the new state."
> 
> If APST is enabled on this disk, what is to stop an autonomous  reverse
> transition from queue activity on the way down?

Nothing.  But once the system is suspending we should not see I/O.

If we see I/O the queue freezing in the original patch Kai Heng and the
previous one from Keith is probably required, although I suspect it
just papers over problems higher up in the queue.  If we don't see I/O
the device is just behaving oddly.