Re: [PATCH v3 2/7] sched/fair: Add cgroup_mode: up

[Peter Zijlstra]

On Fri, Jun 05, 2026 at 02:40:15PM +0200, Peter Zijlstra wrote:
> Instead of calculating the proportional fraction of the group weight for each
> CPU, just give each CPU the full measure, ignoring these pesky SMP problems.
> 
> This makes the SMP cgroup fraction (F_g_n) equal to 1, and ensures a single
> task in a cgroup competes on equal footing to a task in a level above.
> 
> However, as already explored, this is not a very good policy because it gets
> the SMP weight distribution wrong. Included for completeness.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  kernel/sched/debug.c |    5 ++++-
>  kernel/sched/fair.c  |   31 +++++++++++++++++++++++++++++--
>  kernel/sched/sched.h |    1 +
>  3 files changed, 34 insertions(+), 3 deletions(-)
> 
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -271,6 +271,7 @@ static ssize_t sched_dynamic_write(struc
>  	if (mode < 0)
>  		return mode;
>  
> +	__sched_cgroup_mode_update(mode);
>  	sched_dynamic_update(mode);
>  
>  	*ppos += cnt;

Yeez, I'm not sute WTF happened here. Let me go fix that up.