Date: Tue, 21 Jul 2015 08:44:01 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org,
        pjt@google.com, bsegall@google.com, morten.rasmussen@arm.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        umgwanakikbuti@gmail.com, len.brown@intel.com,
        rafael.j.wysocki@intel.com, arjan@linux.intel.com,
        fengguang.wu@intel.com
Subject: Re: [PATCH v10 6/7] sched: Provide runnable_load_avg back to cfs_rq
Message-ID: <20150721004400.GA28512@intel.com>
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 <20150721010346.GA2882@fixme-laptop.cn.ibm.com>
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On Tue, Jul 21, 2015 at 09:08:07AM +0800, Boqun Feng wrote:
> Hi Yuyang,
> 
> On Wed, Jul 15, 2015 at 08:04:41AM +0800, Yuyang Du wrote:
> > The cfs_rq's load_avg is composed of runnable_load_avg and blocked_load_avg.
> > Before this series, sometimes the runnable_load_avg is used, and sometimes
> > the load_avg is used. Completely replacing all uses of runnable_load_avg
> > with load_avg may be too big a leap, i.e., the blocked_load_avg is concerned
> > to result in overrated load. Therefore, we get runnable_load_avg back.
> > 
> > The new cfs_rq's runnable_load_avg is improved to be updated with all of the
> > runnable sched_eneities at the same time, so the one sched_entity updated and
> > the others stale problem is solved.
> > 
> 
> How about tracking cfs_rq's blocked_load_avg instead of
> runnable_load_avg, because, AFAICS:
> 
> cfs_rq->runnable_load_avg = se->avg.load_avg - cfs_rq->blocked_load_avg.

No, cfs_rq->runnable_load_avg = cfs_rq->avg.load_avg - cfs_rq->blocked_load_avg,
without rounding errors and the like.
 
> se is the corresponding sched_entity of cfs_rq. And when we need the
> runnable_load_avg, we just calculate by the expression above.
> 
> This can be thought as a lazy way to update runnable_load_avg, and we
> don't need to modify __update_load_avg any more.

Not lazy at all, but adding (as of now) useless blocked_load_avg and an
extra subtraction.

Or did you forget blocked_load_avg also needs to be updated/decayed as
time elapses?
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