linux-kernel - Re: [Resend patch v8 0/13] use runnable load in schedule balance

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Message-ID: <51C867CF.70908@intel.com>
Date:	Mon, 24 Jun 2013 23:37:51 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Paul Turner <pjt@...gle.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	gregkh@...uxfoundation.org,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>, len.brown@...el.com,
	rafael.j.wysocki@...el.com, jkosina@...e.cz,
	Clark Williams <clark.williams@...il.com>, tony.luck@...el.com,
	keescook@...omium.org, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [Resend patch v8 0/13] use runnable load in schedule balance

On 06/24/2013 06:40 PM, Paul Turner wrote:
>> > Ingo & Peter,
>> >
>> > This patchset was discussed spread and deeply.
>> >
>> > Now just 6th/8th patch has some arguments on them, Paul think it is
>> > better to consider blocked_load_avg in balance, since it is helpful on
>> > some scenarios, but I think on most of scenarios, the blocked_load_avg
>> > just cause load imbalance among cpus. and plus testing show with
>> > blocked_load_avg the performance is just worse on some benchmarks. So, I
>> > still prefer to keep it out of balance.
> I think you have perhaps misunderstood what I was trying to explain.
> 
> I have no problems with not including blocked load in load-balance, in
> fact, I encouraged not accumulating it in an average of averages in
> CPU load.
> 

Many thanks for re-clarification!
> The problem is that your current approach has removed it both from
> load-balance _and_ from shares distribution; isolation matters as much
> as performance in the cgroup case (otherwise you would just not use
> cgroups).  I would expect the latter to have quite negative effects on
> fairness, this is my primary concern.
> 

So the argument is just on patch 'sched/tg: remove blocked_load_avg in balance'. :)

I understand your correctness concern. but blocked_load_avg still will be decayed to zero in few hundreds ms. So such correctness needs just in few hundreds ms. (and cause performance drop)
The blocked_load_avg is decayed on same degree as runnable load, it is a bit overweight since task slept. since it may will be waken up on other cpu. So to relieve this overweight, could we use the half or a quarter weight of blocked_load_avg? like following:

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ddbc19f..395f57c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1358,7 +1358,7 @@ static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
 	struct task_group *tg = cfs_rq->tg;
 	s64 tg_contrib;
 
-	tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;
+	tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg / 2;
 	tg_contrib -= cfs_rq->tg_load_contrib;
 
 	if (force_update || abs64(tg_contrib) > cfs_rq->tg_load_contrib / 8) {

>> >
>> > http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg455196.html
>> >
>> > Is it the time to do the decision or give more comments? Thanks!


-- 
Thanks
    Alex
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