Re: [RFC v3 0/4] Make it easier to measure % in HW sleep state

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11/15/22 21:01, Mario Limonciello wrote:
> Sven van Ashbrook brought a patch to the kernel mailing list that
> attempted to change the reporting level of a s0ix entry issue to a
> different debugging level so that infastructure used by Google could
> better scan logs to catch problems.
> 
> This approach was rejected, but during the conversation another
> suggestion was made by David E. Box to introduce some infrastructure
> into the kernel to report this information.
> 
> As it's information that is reported by both AMD and Intel platforms
> over s2idle, this seems to make sense.
> 
> RFC v1 and v2 introduced two new sysfs files to report the information, but
> Rafael pointed out that there was already a file that could be used on
> Intel platforms: `low_power_idle_system_residency_us`.
> 
> RFC v3 creates this file for AMD platforms and also introduces another file
> that can be used to determine total sleep time:
> `/sys/power/suspend_stats/last_total`.
> 
> With these two files a simple shell script can be run after suspend to
> calculate the percentage.
> 
> ```
>  #!/bin/sh
> total=$(cat /sys/power/suspend_stats/last_total)
> hw=$(cat /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us)
> percent=$(awk -v hw=$hw -v total=$total 'BEGIN { printf "%.2f%%", (hw/total*100) }')
> echo "Last ${total}us suspend cycle spent $percent of the time in a hardware sleep state."
> ```
> 
> A sample run on an AMD platform that was just sleeping with this series on
> top of 6.1-rc5 shows the following:
>  # ./compare.sh
> Last 15699838us suspend cycle spent 98.63% of the time in a hardware sleep state.
> 
> Further discussion to be expected on this series:
> 
> * What last_total will represent from the suspend cycle
> 
> * Whether the semantics of all platforms will be the same for
>   `low_power_idle_system_residency_us`
>   - AMD platforms reset this counter before s2idle entry.  Do Intel? Others?
> 
> * Maybe the *kernel* should be responsible to do the calculation and export
>   a `last_hw_sleep_percent` file instead. Platform differences can be
>   abstracted then within individual drivers.

That (`last_hw_sleep_percent` file) is an interesting proposal,
I can see that being a better interface because as you say this allows
the kernel / platform-drivers to take care of any platform quirks /
weirdness, avoiding any userspace monitoring of this to possibly
give false positive warnings.

Regards,

Hans





> 
> Mario Limonciello (4):
>   PM: Add a sysfs file to represent the total sleep duration
>   platform/x86/intel/pmc: core: Drop check_counters
>   platform/x86/amd: pmc: Report duration of time in deepest hw state
>   platform/x86/amd: pmc: Populate cpuidle sysfs file with hw sleep data
> 
>  Documentation/ABI/testing/sysfs-amd-pmc |  6 ++++++
>  Documentation/ABI/testing/sysfs-power   |  8 ++++++++
>  drivers/platform/x86/amd/pmc.c          | 27 ++++++++++++++++++++++---
>  drivers/platform/x86/intel/pmc/core.c   |  7 ++-----
>  drivers/platform/x86/intel/pmc/core.h   |  1 -
>  include/linux/suspend.h                 |  2 ++
>  kernel/power/main.c                     | 15 ++++++++++++++
>  kernel/power/suspend.c                  |  2 ++
>  kernel/time/timekeeping.c               |  2 ++
>  9 files changed, 61 insertions(+), 9 deletions(-)
>