Re: [PATCH v5 1/3] sched/fair: Introduce the burstable CFS controller

[Peter Zijlstra]

On Mon, May 24, 2021 at 08:42:03PM +0800, changhuaixin wrote:

> >> --- a/kernel/sysctl.c
> >> +++ b/kernel/sysctl.c
> >> @@ -1816,6 +1816,15 @@ static struct ctl_table kern_table[] = {
> >> 		.proc_handler	= proc_dointvec_minmax,
> >> 		.extra1		= SYSCTL_ONE,
> >> 	},
> >> +	{
> >> +		.procname	= "sched_cfs_bw_burst_enabled",
> >> +		.data		= &sysctl_sched_cfs_bw_burst_enabled,
> >> +		.maxlen		= sizeof(unsigned int),
> >> +		.mode		= 0644,
> >> +		.proc_handler	= proc_dointvec_minmax,
> >> +		.extra1		= SYSCTL_ZERO,
> >> +		.extra2		= SYSCTL_ONE,
> >> +	},
> >> #endif
> >> #if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
> >> 	{
> > 
> > What's the purpose of this new sysctl? By default it is disabled because
> > burst==0, only if you set burst to some !0 value does this actually do
> > anything.
> 
> Originally, this is designed to turn burst feature off when the system becomes unstable.
> Guess we can remove this as you have questioned it.

Is stability a concern? This is CFS after all, if we overload, we simply
share time as per usual.

If there is a real use-case for a global knob to limit/disable this I
don't object too much, but then please explicitly mention it.