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Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to config

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  Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to  config Peter Zijlstra <peterz@infradead.org> - 2016-04-28 11:40 +0200
    Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to  config Ingo Molnar <mingo@kernel.org> - 2016-04-28 11:50 +0200
    Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to  config Yuyang Du <yuyang.du@intel.com> - 2016-04-29 06:20 +0200

#1389941 — Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to config

On Tue, Apr 05, 2016 at 12:12:31PM +0800, Yuyang Du wrote:
> The option of increased load resolution (fixed point arithmetic range) is
> unconditionally deactivated with #if 0. But since it may still be used
> somewhere (e.g., in Google), we want to keep this option.
> 
> Regardless, there should be a way to express this option. Considering the
> current circumstances, the reconciliation is we define a config
> CONFIG_CFS_INCREASE_LOAD_RANGE and it depends on FAIR_GROUP_SCHED and
> 64BIT and BROKEN.
> 
> Suggested-by: Ingo Molnar <mingo@kernel.org>

So I'm very tempted to simply, unconditionally, reinstate this larger
range for everything CONFIG_64BIT && CONFIG_FAIR_GROUP_SCHED.

There was but the single claim on increased power usage, nobody could
reproduce / analyze and Google has been running with this for years now.

Furthermore, it seems to be leading to the obvious problems on bigger
machines where we basically run out of precision by the sheer number of
cpus (nr_cpus ~ SCHED_LOAD_SCALE and stuff comes apart quickly).

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#1389948

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Apr 05, 2016 at 12:12:31PM +0800, Yuyang Du wrote:
> > The option of increased load resolution (fixed point arithmetic range) is
> > unconditionally deactivated with #if 0. But since it may still be used
> > somewhere (e.g., in Google), we want to keep this option.
> > 
> > Regardless, there should be a way to express this option. Considering the
> > current circumstances, the reconciliation is we define a config
> > CONFIG_CFS_INCREASE_LOAD_RANGE and it depends on FAIR_GROUP_SCHED and
> > 64BIT and BROKEN.
> > 
> > Suggested-by: Ingo Molnar <mingo@kernel.org>
> 
> So I'm very tempted to simply, unconditionally, reinstate this larger
> range for everything CONFIG_64BIT && CONFIG_FAIR_GROUP_SCHED.
> 
> There was but the single claim on increased power usage, nobody could
> reproduce / analyze and Google has been running with this for years now.
> 
> Furthermore, it seems to be leading to the obvious problems on bigger
> machines where we basically run out of precision by the sheer number of
> cpus (nr_cpus ~ SCHED_LOAD_SCALE and stuff comes apart quickly).

Agreed.

Thanks,

	Ingo

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#1390722

On Thu, Apr 28, 2016 at 11:37:33AM +0200, Peter Zijlstra wrote:
> On Tue, Apr 05, 2016 at 12:12:31PM +0800, Yuyang Du wrote:
> > The option of increased load resolution (fixed point arithmetic range) is
> > unconditionally deactivated with #if 0. But since it may still be used
> > somewhere (e.g., in Google), we want to keep this option.
> > 
> > Regardless, there should be a way to express this option. Considering the
> > current circumstances, the reconciliation is we define a config
> > CONFIG_CFS_INCREASE_LOAD_RANGE and it depends on FAIR_GROUP_SCHED and
> > 64BIT and BROKEN.
> > 
> > Suggested-by: Ingo Molnar <mingo@kernel.org>
> 
> So I'm very tempted to simply, unconditionally, reinstate this larger
> range for everything CONFIG_64BIT && CONFIG_FAIR_GROUP_SCHED.
> 
> There was but the single claim on increased power usage, nobody could
> reproduce / analyze and Google has been running with this for years now.
> 
> Furthermore, it seems to be leading to the obvious problems on bigger
> machines where we basically run out of precision by the sheer number of
> cpus (nr_cpus ~ SCHED_LOAD_SCALE and stuff comes apart quickly).
 
Great.

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