RE: [PATCH] nvme: lower default APST max latency to 25ms

[Alexey Bogoslavsky]

> -----Original Message-----
> From: Ferran Duarri <ferran.duarri@xxxxxx> 
> Sent: Monday, August 31, 2026 4:17 PM
> To: Alexey Bogoslavsky <Alexey.Bogoslavsky@xxxxxxxxxxx>; Keith Busch <kbusch@xxxxxxxxxx>; Jens Axboe <axboe@xxxxxxxxx>; Christoph Hellwig <hch@xxxxxx>; Sagi Grimberg <sagi@xxxxxxxxxxx>
> Cc: Yehuda Hahn <Yehuda.Hahn@xxxxxxxxxxx>; linux-nvme@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Ferran Duarri <ferran.duarri@xxxxxx>
> Subject: Re: [PATCH] nvme: lower default APST max latency to 25ms

> Alexey - thanks, that's a real point I hadn't considered: if EXLAT is
> deliberately inflated to keep Windows on ps3, the 100ms default isn't a bug,
> it's aligned with what vendors actually tuned for.

> The measurement itself I think still holds - it's reading what the drive's
> live APST table targets, not just trusting the label, and the wake cost at
> ps4 was real regardless of why 43ms is the number on the tin. But that's a
> different question from whether Linux should default away from it.

> What's the OEM precedent you mentioned - did lowering the bound before break
> something specific, or was it more general pushback? Trying to understand if
> this needs to stay a boot-time opt-in (which it already is via
> default_ps_max_latency_us) rather than ever being a compiled default, on any
> hardware.

Hi, Ferran,
The immediate reason for revising the previous algorithm was failure to
meet Chromebook power consumption requirements (as mentioned in commit
ebd8a93). But the problem is a generic one, excessively high power
consumption is never OK and will occasionally be caught by OEMs during
device qualification tests.
Regards,
Alexey

> Also - sorry for the fourth copy of this patch landing in your inbox on the
> 28th. That was a bookkeeping failure on my end, not a deliberate re-post; it
> went out after your reply had already arrived and should not have.

That's OK)

> Cheers,
> Ferran