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

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Message-ID: <20151109161916.1400a0b4@icelake>
Date:	Mon, 9 Nov 2015 16:19:16 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

On Fri, 6 Nov 2015 15:49:29 -0800
Jacob Pan <jacob.jun.pan@...ux.intel.com> wrote:

> > 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.
ok, I added a check for softirq_pending and a retry. seems to work. Now
idle injection will allow softirq and softirqd to run. The caveat is
that during that injection period, if softirqd does not run for the
entire duration, other normal tasks would also run during forced idle.
But just for that period. I guess we have to strike for the right
balance for QoS and overhead. For most workload, pending softirq is
rare so the tasks slip under softirqd are also rare. Will send out V2
soon.

Thanks,

Jacob
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