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

[rjw@rjwysocki.net (Rafael J. Wysocki)]

On Thursday, July 25, 2019 4:52:10 PM CEST Keith Busch wrote:
> On Thu, Jul 25, 2019@02:51:41AM -0700, Rafael J. Wysocki wrote:
> > Hi Keith,
> > 
> > Unfortunately,
> > 
> > commit d916b1be94b6dc8d293abed2451f3062f6af7551
> > Author: Keith Busch <keith.busch at 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:-