Date: Fri, 29 Apr 2016 04:34:05 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, bsegall@google.com,
        pjt@google.com, morten.rasmussen@arm.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, lizefan@huawei.com, umgwanakikbuti@gmail.com
Subject: Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to
 config
Message-ID: <20160428203405.GE16093@intel.com>
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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.