From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Rafael Wysocki <rafael.j.wysocki@intel.com>,
Len Brown <len.brown@intel.com>,
Andi Kleen <andi.kleen@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Paul Turner <pjt@google.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Eduardo Valentin <edubezval@gmail.com>,
Punit Agrawal <punit.agrawal@arm.com>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
jacob.jun.pan@linux.intel.com
Subject: Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection
Date: Tue, 10 Nov 2015 08:50:55 -0800 [thread overview]
Message-ID: <20151110085055.67bdb1fa@icelake> (raw)
In-Reply-To: <20151110163646.GG17308@twins.programming.kicks-ass.net>
On Tue, 10 Nov 2015 17:36:46 +0100
Peter Zijlstra <peterz@infradead.org> wrote:
> > The downside is that we need to restart the timers every time if
> > user were to change injection parameters, i.e. duration and percent.
> > Or do locking which might be too expensive. In the previous
> > approach, it will naturally catch up the parameter change.
>
> Why? the timer will fire and observe the new value for reprogramming
> the next period. All you need to do is to ensure whole values are
> written/read -- ie. avoid load/store tearing.
Different per CPU timer may intercept parameter changes at slightly
different time, so there is a race condition such that some CPUs may
catch the period change later by one period, which results in a correct
period change but at a different time, i.e. out of sync.
Jacob
next prev parent reply other threads:[~2015-11-10 16:51 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-10 0:21 [RFC PATCH v2 0/3] CFS idle injection Jacob Pan
2015-11-10 0:21 ` [RFC PATCH v2 1/3] ktime: add a roundup function Jacob Pan
2015-11-10 0:21 ` [RFC PATCH v2 2/3] timer: relax tick stop in idle entry Jacob Pan
2015-11-10 0:21 ` [RFC PATCH v2 3/3] sched: introduce synchronized idle injection Jacob Pan
2015-11-10 13:23 ` Peter Zijlstra
2015-11-10 14:01 ` Jacob Pan
2015-11-10 14:58 ` Peter Zijlstra
2015-11-10 16:28 ` Jacob Pan
2015-11-10 16:36 ` Peter Zijlstra
2015-11-10 16:50 ` Jacob Pan [this message]
2015-11-10 17:00 ` Peter Zijlstra
2015-11-10 17:14 ` Jacob Pan
2015-11-10 18:41 ` Jacob Pan
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