NVMe APST high latency power states being skipped

[Andy Lutomirski]

On Tue, Jun 6, 2017 at 2:54 AM, Christoph Hellwig <hch at infradead.org> wrote:
> On Fri, Jun 02, 2017 at 12:13:37AM -0700, Christoph Hellwig wrote:
>> > Maybe add an extra knob which can directly control deepest allow power
>> > state? Userspace tools can control deepest power state through this
>> > knob.
>>
>> I'd prefer that things work out of the box.  I'd be tempted to just
>> bump up the latency requirement to cover the device, but if Andy
>> doesn't like that in general we could add a quirk for this device
>> to at least allow it to use deep power states.
>
> Kai, can you send the patch to bump default_ps_max_latency_us to
> reasonably high value that all the devices you are testing are
> able to use PS3/4?

I'm starting to think we should ignore enlat and only consider exlat
when we interpret the requested max latency.  If I find some time,
I'll try to write a little benchmark to see how drives actually
behave.

Given that we've seen enlat as high as 1s, I don't think we want to
start setting the default latency over 1s.

--Andy