From mboxrd@z Thu Jan 1 00:00:00 1970 From: james_p_freyensee@linux.intel.com (J Freyensee) Date: Fri, 02 Sep 2016 14:15:05 -0700 Subject: [PATCH v2 3/3] nvme: Enable autonomous power state transitions In-Reply-To: <6e6c3cd47858160bf8e34f2edb481c0ef5092d5b.1472594203.git.luto@kernel.org> References: <6e6c3cd47858160bf8e34f2edb481c0ef5092d5b.1472594203.git.luto@kernel.org> Message-ID: <1472850905.2946.20.camel@linux.intel.com> On Tue, 2016-08-30@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). Now from? nvme id-ctrl /dev/nvme0 (or nvme1) NVME Identify Controller: vid?????: 0x8086 ssvid???: 0x8086 sn??????: CVFT41720018800HGN?? mn??????: INTEL SSDPE2MD800G4????????????????????? fr??????: 8DV10151 rab?????: 0 ieee????: 5cd2e4 cmic????: 0 mdts????: 5 cntlid??: 0 ver?????: 0 rtd3r???: 0 rtd3e???: 0 oaes????: 0 oacs????: 0x6 acl?????: 3 aerl????: 3 frmw????: 0x2 lpa?????: 0x2 elpe????: 63 npss????: 0 avscc???: 0 apsta???: 0 <----- the Fultondales don't support apst. But I'd still like to ask the dumb question :-). > > On hardware without APST support, apst_max_latency_us will not be > exposed in sysfs. Not sure that is true, as from what I see so far, Fultondales don't support apst yet I still see: [root at nvme-fabric-host01 nvme-cli]# cat /sys/module/nvme_core/parameters/apst_max_latency_us 25000 > > In theory, the device can expose "default" APST table, but this > doesn't seem to function correctly on my device (Samsung 950), nor > does it seem particularly useful.??There is also an optional > mechanism by which a configuration can be "saved" so it will be > automatically loaded on reset.??This can be configured from > userspace, but it doesn't seem useful to support in the driver. > > On my laptop, enabling APST seems to save nearly 1W. > > The hardware tables can be decoded in userspace with nvme-cli. > 'nvme id-ctrl /dev/nvmeN' will show the power state table and > 'nvme get-feature -f 0x0c -H /dev/nvme0' will show the current APST > configuration. nvme get-feature -f 0x0c -H /dev/nvme0 isn't working for me, I get a: [root at nvme-fabric-host01 nvme-cli]# ./nvme get-feature -f 0x0c -H /dev/nvme0 NVMe Status:INVALID_FIELD(2) I don't have the time right now to investigate further, but I'll assume it's because I have Fultondales (though I would have thought this patch would have provided enough code for the latest nvme-cli code to do this new get-feature as-is). Jay