Re: [PATCH 3/8] x86/itmt: Move the "sched_itmt_enabled" sysctl to debugfs

[Tim Chen]

On Fri, 2024-12-13 at 09:31 +0530, K Prateek Nayak wrote:
> Hello Tim,
> 
> Thank you for reviewing the series.
> 
> On 12/13/2024 12:45 AM, Tim Chen wrote:
> > On Wed, 2024-12-11 at 18:55 +0000, K Prateek Nayak wrote:
> > > "sched_itmt_enabled" was only introduced as a debug toggle for any funky
> > > ITMT behavior. Move the sysctl controlled from
> > > "/proc/sys/kernel/sched_itmt_enabled" to debugfs at
> > > "/sys/kernel/debug/x86/sched_itmt_enabled" with a notable change that a
> > > cat on the file will return "Y" or "N" instead of "1" or "0" to
> > > indicate that feature is enabled or disabled respectively.
> > > 
> > 
> > Valid values of setting "sched_itmt_enabled" likewise change from "1" or "0"
> > to "Y" or "N".
> 
> Turns out you can still use "1" and "0". Running:
> 
>      echo Y > /sys/kernel/debug/sched/verbose
>      echo "sched_itmt_enabled: $(cat /sys/kernel/debug/x86/sched_itmt_enabled)";
>      for i in 0 1 N Y;
>      do
>          echo "Writing $i to /sys/kernel/debug/x86/sched_itmt_enabled";
>          echo $i > /sys/kernel/debug/x86/sched_itmt_enabled;
>          echo "sched_itmt_enabled: $(cat /sys/kernel/debug/x86/sched_itmt_enabled)";
>          echo "sched domain flags:";
>          cat /sys/kernel/debug/sched/domains/cpu0/domain*/flags;
>          echo;
>      done
> 
> Yields the following output on my system:
> 
>      sched_itmt_enabled: Y
> 
>      Writing 0 to /sys/kernel/debug/x86/sched_itmt_enabled
>      sched_itmt_enabled: N
>      sched domain flags:
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_PREFER_SIBLING
> 
>      Writing 1 to /sys/kernel/debug/x86/sched_itmt_enabled
>      sched_itmt_enabled: Y
>      sched domain flags:
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_LLC SD_ASYM_PACKING SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_ASYM_PACKING SD_PREFER_SIBLING
> 
>      Writing N to /sys/kernel/debug/x86/sched_itmt_enabled
>      sched_itmt_enabled: N
>      sched domain flags:
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_PREFER_SIBLING
> 
>      Writing Y to /sys/kernel/debug/x86/sched_itmt_enabled
>      sched_itmt_enabled: Y
>      sched domain flags:
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_LLC SD_ASYM_PACKING SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_ASYM_PACKING SD_PREFER_SIBLING
> 
> Would you like me to extend that note as:
> 
>      ... with a notable change that a
>      cat on the file will return "Y" or "N" instead of "1" or "0" to
>      indicate that feature is enabled or disabled respectively. User can
>      either write "0" or "1" to toggle the feature off when enabled, or
>      "1" or "Y" to toggle the feature on when disabled.
> 
> for the record?
> 
> 
Sure.  Thanks.

Tim