linux-kernel - Re: [PATCH 0/5] nvme APST fixes/improvements for 4.11

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Date:   Wed, 19 Apr 2017 20:55:47 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <keith.busch@...el.com>
Subject: Re: [PATCH 0/5] nvme APST fixes/improvements for 4.11

On Wed, Apr 19, 2017 at 8:10 PM, Jens Axboe <axboe@...nel.dk> wrote:
> On Wed, Apr 19 2017, Andy Lutomirski wrote:
>> Sorry for waiting so long for this.  I was waiting for feedback from
>> Samsung, but they haven't root-caused the issue yet, and I should
>> have just done this from the beginning.
>>
>> This series makes APST more debuggable and updates the quirk list.
>> The quirks I'm aware of are:
>>
>>  - Samsung 950 series SSDs in Dell XPS 15 9550 and Precision 5510
>>    laptops (which are essentially the same laptop) can lose their
>>    PCIe link if they're allowed to use the deepest APST state.
>>    Samsung engineers have an affected system and are working on
>>    it.  The same exact SSDs in other machines (even an XPS 13)
>>    seem to work fine.
>>
>>  - One Toshiba device malfunctions if APST is used at all.
>
> You need to split this series in two, patches 1-3 can wait. For 4.11,
> all we need to do is turn off APST on any device that potentially has
> this problem.
>
>> One thing that improves my confidence that there aren't too many
>> more problems with APST is that Ubuntu has backported APST to Zesty,
>> so it's already gotten a bit of testing in a widely used (if very
>> new) release.
>
> Honestly, I think the best path for 4.11 is to turn off APST by default,
> make it opt-in instead. I don't share your optimism here, as I made
> clear back from before we even merged this feature.
>
>

I can make it so that force_apst=0 means no APST and force_apst=1 mean
yes APST and we could try again with a quirk list for 4.12.  There's a
decent chance that a few more weeks with Ubuntu having APST on will
shake out all the problems fairly quickly.

--Andy