Re: [Regression] Commit "nvme/pci: Use host managed power state for suspend" has problems

Rafael J. Wysocki
2019-07-25T19:49:03Z

On Thursday, July 25, 2019 4:52:10 PM CEST Keith Busch wrote:
> On Thu, Jul 25, 2019 at 02:51:41AM -0700, Rafael J. Wysocki wrote:
> > Hi Keith,
> >
> > Unfortunately,
> >
> > commit d916b1be94b6dc8d293abed2451f3062f6af7551
> > Author: Keith Busch <keith.busch@intel.com>
> > Date: Thu May 23 09:27:35 2019 -0600
> >
> > nvme-pci: use host managed power state for suspend
> >
> > doesn't universally improve things. In fact, in some cases it makes things worse.
> >
> > For example, on the Dell XPS13 9380 I have here it prevents the processor package
> > from reaching idle states deeper than PC2 in suspend-to-idle (which, of course, also
> > prevents the SoC from reaching any kind of S0ix).
> >
> > That can be readily explained too. Namely, with the commit above the NVMe device
> > stays in D0 over suspend/resume, so the root port it is connected to also has to stay in
> > D0 and that "blocks" package C-states deeper than PC2.
> >
> > In order for the root port to be able to go to D3, the device connected to it also needs
> > to go into D3, so it looks like (at least on this particular machine, but maybe in
> > general), both D3 and the NVMe-specific PM are needed.
> >
> > I'm not sure what to do here, because evidently there are systems where that commit
> > helps. I was thinking about adding a module option allowing the user to override the
> > default behavior which in turn should be compatible with 5.2 and earlier kernels.
>
> Darn, that's too bad. I don't think we can improve one thing at the
> expense of another, so unless we find an acceptable criteria to select
> what low power mode to use, I would be inclined to support a revert or
> a kernel option to default to the previous behavior.
>
> One thing we might check before using NVMe power states is if the lowest
> PS is non-operational with MP below some threshold. What does your device
> report for:
>
> nvme id-ctrl /dev/nvme0

NVME Identify Controller:
vid : 0x1c5c
ssvid : 0x1c5c
sn : MS92N171312902J0N
mn : PC401 NVMe SK hynix 256GB
fr : 80007E00
rab : 2
ieee : ace42e
cmic : 0
mdts : 5
cntlid : 1
ver : 10200
rtd3r : 7a120
rtd3e : 1e8480
oaes : 0x200
ctratt : 0
oacs : 0x17
acl : 7
aerl : 3
frmw : 0x14
lpa : 0x2
elpe : 255
npss : 4
avscc : 0x1
apsta : 0x1
wctemp : 352
cctemp : 354
mtfa : 0
hmpre : 0
hmmin : 0
tnvmcap : 0
unvmcap : 0
rpmbs : 0
edstt : 10
dsto : 0
fwug : 0
kas : 0
hctma : 0
mntmt : 0
mxtmt : 0
sanicap : 0
hmminds : 0
hmmaxd : 0
nsetidmax : 0
anatt : 0
anacap : 0
anagrpmax : 0
nanagrpid : 0
sqes : 0x66
cqes : 0x44
maxcmd : 0
nn : 1
oncs : 0x1f
fuses : 0x1
fna : 0
vwc : 0x1
awun : 7
awupf : 7
nvscc : 1
acwu : 7
sgls : 0
mnan : 0
subnqn :
ioccsz : 0
iorcsz : 0
icdoff : 0
ctrattr : 0
msdbd : 0
ps 0 : mp:6.00W operational enlat:5 exlat:5 rrt:0 rrl:0
rwt:0 rwl:0 idle_power:- active_power:-
ps 1 : mp:3.80W operational enlat:30 exlat:30 rrt:1 rrl:1
rwt:1 rwl:1 idle_power:- active_power:-
ps 2 : mp:2.40W operational enlat:100 exlat:100 rrt:2 rrl:2
rwt:2 rwl:2 idle_power:- active_power:-
ps 3 : mp:0.0700W non-operational enlat:1000 exlat:1000 rrt:3 rrl:3
rwt:3 rwl:3 idle_power:- active_power:-
ps 4 : mp:0.0070W non-operational enlat:1000 exlat:5000 rrt:3 rrl:3
rwt:3 rwl:3 idle_power:- active_power:-