From: Thomas Gleixner <tglx@linutronix.de>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
Preeti U Murthy <preeti@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Viresh Kumar <viresh.kumar@linaro.org>, LKP <lkp@01.org>,
LKML <linux-kernel@vger.kernel.org>,
"Zhang, Rui" <rui.zhang@intel.com>,
Frederic Weisbecker <frederic@kernel.org>,
Eduardo Valentin <edubezval@gmail.com>
Subject: Re: [PATCH] tick/powerclamp: Remove tick_nohz_idle abuse
Date: Thu, 18 Dec 2014 22:12:57 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1412182209010.17382@nanos> (raw)
In-Reply-To: <20141218115239.53d17e39@jacob-VirtualBox>
On Thu, 18 Dec 2014, Jacob Pan wrote:
> OK I agree, also as I mentioned earlier, Peter already has a patch for
> consolidated idle loop and remove tick_nohz_idle_enter/exit call from
> powerclamp driver. I have been working on a few tweaks to maintain the
> functionality and efficiency with the consolidated idle loop.
> We can apply the patches on top of yours.
No. This is equally wrong as I pointed out before. The 'unified' idle
loop is still fake and just pretending to be idle.
If simple standard interfaces like cpu_idle() are not working from
idle code anymore then this simply stinks. And that's what any fake
idle thread will do.
The whole approach is wrong. Implement a sched fair throttler and you
can avoid the whoile trainwreck.
> > 1. Queue a deferable periodic timer whose handler checks if idle
> > needs to be injected. If so, it sets rq->need_throttle for the cpu.
> > If its already in the fake idle period, it clears rq->need_throttle
> > and sets need_resched.
> >
> The key to powerclamp driver is to achieve package level idle
> states, which implies synchronized idle injection. From
> power/performance standpoint, only package level idle states is worth
> injection.
Then use a synchronized non deferrable timer on all cpus. It's simple
enough.
Thanks,
tglx
next prev parent reply other threads:[~2014-12-18 21:13 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-18 10:51 [PATCH] tick/powerclamp: Remove tick_nohz_idle abuse Thomas Gleixner
2014-12-18 14:01 ` Eduardo Valentin
2014-12-18 14:43 ` Thomas Gleixner
2014-12-18 17:28 ` Preeti U Murthy
[not found] ` <DD415AA12F8FF042BF4EA69DF123C1478AF91730@ORSMSX101.amr.corp.intel.com>
2014-12-18 19:52 ` Jacob Pan
2014-12-18 21:12 ` Thomas Gleixner [this message]
2014-12-19 18:39 ` Jacob Pan
2014-12-19 19:56 ` Thomas Gleixner
2014-12-20 1:31 ` Preeti U Murthy
2014-12-23 2:57 ` Jacob Pan
2014-12-31 5:04 ` Preeti U Murthy
2014-12-19 13:09 ` [tip:timers/urgent] " tip-bot for Thomas Gleixner
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