linux-kernel - Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

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Date:	Fri, 6 Nov 2015 15:49:29 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

On Fri, 6 Nov 2015 08:45:10 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Nov 05, 2015 at 03:36:25PM -0800, Jacob Pan wrote:
> 
> > I did some testing with the code below, it shows random
> > [  150.442597] NOHZ: local_softirq_pending 02
> > [  153.032673] NOHZ: local_softirq_pending 202
> > [  153.203785] NOHZ: local_softirq_pending 202
> > [  153.206486] NOHZ: local_softirq_pending 282
> > I recalled that was why i checked for local_softirq_pending in the
> > initial patch, still trying to find out how we can avoid that. These
> > also causes non stop sched ticks in the inner idle loop.
> 
> Check the softirq stuff before calling throttle ?

yes, played with it but it seems there are other cases causing pending
softirq in idle in addition to throttle. I still haven't figure it out,
this problem only shows up in heavy irq, network load. e.g. compile
kernel over NFS. Debugging.
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