linux-kernel - Re: [PATCH v4 0/3] nvme power saving

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Date:   Fri, 16 Sep 2016 17:49:55 -0700
From:   J Freyensee <james_p_freyensee@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>
Cc:     linux-nvme@...ts.infradead.org, Christoph Hellwig <hch@....de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/3] nvme power saving

On Fri, 2016-09-16 at 11:16 -0700, Andy Lutomirski wrote:
> Hi all-
> 
> Here's v4 of the APST patch set.  The biggest bikesheddable thing (I
> think) is the scaling factor.  I currently have it hardcoded so that
> we wait 50x the total latency before entering a power saving state.
> On my Samsung 950, this means we enter state 3 (70mW, 0.5ms entry
> latency, 5ms exit latency) after 275ms and state 4 (5mW, 2ms entry
> latency, 22ms exit latency) after 1200ms.  I have the default max
> latency set to 25ms.
> 
> FWIW, in practice, the latency this introduces seems to be well
> under 22ms, but my benchmark is a bit silly and I might have
> measured it wrong.  I certainly haven't observed a slowdown just
> using my laptop.
> 
> This time around, I changed the names of parameters after Jay
> Frayensee got confused by the first try.  Now they are:
> 
>  - ps_max_latency_us in sysfs: actually controls it.
>  - nvme_core.default_ps_max_latency_us: sets the default.
> 
> Yeah, they're mouthfuls, but they should be clearer now.
> 

I took the patches and applied them to one of my NVMe fabric hosts on
my NVMe-over-Fabrics setup.  Basically, it doesn't test much other than
Andy's explanation that "ps_max_latency_us" does not appear in any of
/sys/block/nvmeXnY sysfs nodes (I have 7) so seems good to me on this
front.

Tested-by: Jay Freyensee <james_p_freyensee@...ux.intel.com>
[jpf: defaults benign to NVMe-over-Fabrics]