linux-kernel - Re: [PATCH 3/3] nvme: Enable autonomous power state transitions

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Message-ID: <CALCETrUM0rUOk52VUEeZge-t3Mrz7=d8WqpNOghyFpzYkdY38w@mail.gmail.com>
Date:   Fri, 2 Sep 2016 11:50:59 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     J Freyensee <james_p_freyensee@...ux.intel.com>
Cc:     Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>, linux-nvme@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] nvme: Enable autonomous power state transitions

On Fri, Sep 2, 2016 at 11:11 AM, J Freyensee
<james_p_freyensee@...ux.intel.com> wrote:
>
>> > >
>> > >
>> > > >
>> > > > +     /*
>> > > > +      * By default, allow up to 25ms of APST-induced
>> > > > latency.  This will
>> > > > +      * have no effect on non-APST supporting controllers
>> > > > (i.e.
>> > > > any
>> > > > +      * controller with APSTA == 0).
>> > > > +      */
>> > > > +     ctrl->apst_max_latency_ns = 25000000;
>> > >
>> > > Is it possible to make that a #define please?
>> >
>> > I'll make it a module parameter as Keith suggested.
>>
>> One question, though: should we call this and the sysfs parameter
>> apst_max_latency or should it be more generically
>> power_save_max_latency?  The idea is that we might want to support
>> non-automonous transitions some day or even runtime D3.  Or maybe
>> those should be separately configured if used.
>
> I read the spec and reviewed your latest patchset.  Personally for me I
> like having the field names from the NVMe spec in the names of the
> Linux implementation because it makes it easier to find and relate the
> two.  So apst_max_latency makes more sense to me, as this is a
> 'apst'(e/a) NVMe feature.
>

It's not really an APST feature, though -- it's just the maximum
(entry + exit) latency from the power state table.  So if we every
supported non-APST power state transitions, we could use the same type
of policy.

I'm not really arguing for changing it, though, and I personally have
no plans to implement a non-autonomous policy.

--Andy