Messages in this thread | | | Subject | Re: [PATCH v2 3/3] nvme: Enable autonomous power state transitions | From | J Freyensee <> | Date | Fri, 02 Sep 2016 15:23:05 -0700 |
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On Fri, 2016-09-02 at 14:43 -0700, Andy Lutomirski wrote: > On Fri, Sep 2, 2016 at 2:15 PM, J Freyensee > <james_p_freyensee@linux.intel.com> wrote: > > > > On Tue, 2016-08-30 at 14:59 -0700, Andy Lutomirski wrote: > > > > > > NVME devices can advertise multiple power states. These states > > > can > > > be either "operational" (the device is fully functional but > > > possibly > > > slow) or "non-operational" (the device is asleep until woken up). > > > Some devices can automatically enter a non-operational state when > > > idle for a specified amount of time and then automatically wake > > > back > > > up when needed. > > > > > > The hardware configuration is a table. For each state, an entry > > > in > > > the table indicates the next deeper non-operational state, if > > > any, > > > to autonomously transition to and the idle time required before > > > transitioning. > > > > > > This patch teaches the driver to program APST so that each > > > successive non-operational state will be entered after an idle > > > time > > > equal to 100% of the total latency (entry plus exit) associated > > > with > > > that state. A sysfs attribute 'apst_max_latency_us' gives the > > > maximum acceptable latency in ns; non-operational states with > > > total > > > latency greater than this value will not be used. As a special > > > case, apst_max_latency_us=0 will disable APST entirely. > > > > May I ask a dumb question? > > > > How does this work with multiple NVMe devices plugged into a > > system? I > > would have thought we'd want one apst_max_latency_us entry per NVMe > > controller for individual control of each device? I have two > > Fultondale-class devices plugged into a system I tried these > > patches on > > (the 4.8-rc4 kernel) and I'm not sure how the single > > /sys/module/nvme_core/parameters/apst_max_latency_us would work per > > my > > 2 devices (and the value is using the default 25000). > > > > Ah, I faked you out :( > > The module parameter (nvme_core/parameters/apst_max_latency_us) just > sets the default for newly probed devices. The actual setting is in > /sys/devices/whatever (symlinked from /sys/block/nvme0n1/devices, for > example). Perhaps I should name the former > default_apst_max_latency_us.
It would certainly be more describable to understand what the entry is for, but then the name is also getting longer.
Just "default_apst_latency_us"? Or maybe it's probably fine as-is.
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