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.