linux-kernel - Re: A few questions and issues with dynticks, NOHZ and powertop

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Message-ID: <4BB95C33.1050706@linux.intel.com>
Date:	Sun, 04 Apr 2010 20:42:43 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Dominik Brodowski <linux@...inikbrodowski.net>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Adam Belay <abelay@...ell.com>,
	Len Brown <len.brown@...el.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: A few questions and issues with dynticks, NOHZ and powertop

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.
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