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Date: Mon, 5 Apr 2010 22:41:43 +0200
From: Dominik Brodowski <linux@dominikbrodowski.net>
To: Arjan van de Ven <arjan@linux.intel.com>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Adam Belay <abelay@novell.com>, Len Brown <len.brown@intel.com>,
       linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
       Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
       Alan Stern <stern@rowland.harvard.edu>
Subject: Re: A few questions and issues with dynticks, NOHZ and powertop
Message-ID: <20100405204143.GB23159@comet.dominikbrodowski.net>
Mail-Followup-To: Dominik Brodowski <linux@dominikbrodowski.net>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Adam Belay <abelay@novell.com>, Len Brown <len.brown@intel.com>,
	linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
	Alan Stern <stern@rowland.harvard.edu>
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On Sun, Apr 04, 2010 at 08:42:43PM -0700, Arjan van de Ven wrote:
> On 4/4/2010 3:47, Dominik Brodowski wrote:
> >Hey,
> >
> >On Sat, Apr 03, 2010 at 04:53:26PM -0700, Dmitry Torokhov wrote:
> >>On Sun, Apr 04, 2010 at 12:33:28AM +0200, Dominik Brodowski wrote:
> >>>
> >>>4) SynPS/2 touchpad:
> >>>Why does moving the touchpad lead to sooo many IRQs? I can't look as fast
> >>>as the mouse pointer seems to get new data:
> >>>   62,5% (473,1)<interrupt>  : PS/2 keyboard/mouse/touchpad
> >>>
> >>
> >>80 pps @ 6 bytes/packet = 480 interrupts/sec.
> >>
> >>You can try using psmouse.rate=40 to limit it to 40 pps which should
> >>bring it to the rate of standard PS/2 mouse at the expense of
> >>sensitivity...
> >
> >as a sidenote: if we know -- like here -- that the next IRQ will be issued
> >soon, in approximately 1.75 ms (well, at least on my system), might it make
> >sense to make tick_nohz_get_sleep_length() smarter to know about this?
> 
> yes and no.
> 
> if you are very sure (95%+ or so) then absolutely it needs to know about this
> so that the C state selection code can make a better decision.
> Right now it tries to look at history to guess this delay.
> 
> Unfortunately we do not currently have such a concept in the code to make this
> work... but it'd be really nice to have.

Dmitry, are we "very sure" in this touchpad case?

Best,
	Dominik

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