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== Comment: #0 - Michael Ranweiler <mranw...@us.ibm.com> - 2018-09-04
00:50:14 ==
The CPUs remain in snooze state on an idle system when only the shallow
states disabled resulting in increased power consumption.
The commit 78eaa10f027c ("cpuidle: powernv/pseries: Auto-promotion of snooze
to deeper idle state") introduced a timeout for the snooze idle state so that
it could be eventually be promoted to a deeper idle state. The snooze
timeout value is static and set to the target residency of the next idle
state, which would train the cpuidle governor to pick the next idle state
eventually.
The unfortunate side-effect of this is that if the next idle state(s) is
disabled, the CPU will forever remain in snooze, despite the fact that the
system is completely idle, and other deeper idle states are available.
This patch fixes the issue by dynamically setting the snooze timeout to the
target residency of the next enabled state on the device.
Before Patch:
POWER8 : Only nap disabled.
$ cpupower monitor sleep 30
sleep took 30.01297 seconds and exited with status 0
|Idle_Stats
PKG |CORE|CPU | snoo | Nap | Fast
0| 8| 0| 96.41| 0.00| 0.00
0| 8| 1| 96.43| 0.00| 0.00
0| 8| 2| 96.47| 0.00| 0.00
0| 8| 3| 96.35| 0.00| 0.00
0| 8| 4| 96.37| 0.00| 0.00
0| 8| 5| 96.37| 0.00| 0.00
0| 8| 6| 96.47| 0.00| 0.00
0| 8| 7| 96.47| 0.00| 0.00
POWER9: Shallow states (stop0lite, stop1lite, stop2lite, stop0, stop1, stop2)
disabled:
$ cpupower monitor sleep 30
sleep took 30.05033 seconds and exited with status 0
|Idle_Stats
PKG |CORE|CPU | snoo | stop | stop | stop | stop | stop | stop | stop |
stop
0| 16| 0| 89.79| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00|
0.00
0| 16| 1| 90.12| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00|
0.00
0| 16| 2| 90.21| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00|
0.00
0| 16| 3| 90.29| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00|
0.00
After Patch:
POWER8 : Only nap disabled.
$ cpupower monitor sleep 30
sleep took 30.01200 seconds and exited with status 0
|Idle_Stats
PKG |CORE|CPU | snoo | Nap | Fast
0| 8| 0| 16.58| 0.00| 77.21
0| 8| 1| 18.42| 0.00| 75.38
0| 8| 2| 4.70| 0.00| 94.09
0| 8| 3| 17.06| 0.00| 81.73
0| 8| 4| 3.06| 0.00| 95.73
0| 8| 5| 7.00| 0.00| 96.80
0| 8| 6| 1.00| 0.00| 98.79
0| 8| 7| 5.62| 0.00| 94.17
POWER9: Shallow states (stop0lite, stop1lite, stop2lite, stop0, stop1,
stop2) disabled:
$ cpupower monitor sleep 30
sleep took 30.02110 seconds and exited with status 0
|Idle_Stats
PKG |CORE|CPU | snoo | stop | stop | stop | stop | stop | stop | stop |
stop
0| 0| 0| 0.69| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 9.39|
89.70
0| 0| 1| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.05|
93.21
0| 0| 2| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00|
89.93
0| 0| 3| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00| 0.00|
93.26
This fix (commit 0a4ec6aa035a "cpuidle: powernv: Fix promotion from snooze if
next state disabled") is in the -next branch of the powerpc tree and
upstream:https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/cpuidle/cpuidle-powernv.c?id=0a4ec6aa035a52c422eceb2ed51ed88392a3d6c2
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
Status: New
** Tags: architecture-ppc64le bugnameltc-171057 severity-critical
targetmilestone-inin---
--
Ubuntu18.04.1: cpuidle: powernv: Fix promotion from snooze if next state
disabled (performance)
https://bugs.launchpad.net/bugs/1790602
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