Re: [PATCH RESEND] sched/nohz: Add HRTICK_BW for using cfs bandwidth with nohz_full

[Peter Zijlstra]

On Thu, May 18, 2023 at 09:20:38AM -0400, Phil Auld wrote:
> CFS bandwidth limits and NOHZ full don't play well together.  Tasks
> can easily run well past their quotas before a remote tick does
> accounting.  This leads to long, multi-period stalls before such
> tasks can run again.  Use the hrtick mechanism to set a sched
> tick to fire at remaining_runtime in the future if we are on
> a nohz full cpu, if the task has quota and if we are likely to
> disable the tick (nr_running == 1).  This allows for bandwidth
> accounting before tasks go too far over quota.
> 
> A number of container workloads use a dynamic number of real
> nohz tasks but also have other work that is limited which ends
> up running on the "spare" nohz cpus.  This is an artifact of
> having to specify nohz_full cpus at boot. Adding this hrtick
> resolves the issue of long stalls on these tasks.
> 
> Add the sched_feat HRTICK_BW off by default to allow users to
> enable this only when needed.

OMG; so because NOHZ_FULL configuration sucks, we add hacks on?