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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@linux.intel.com>
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To: Dominik Brodowski <linux@dominikbrodowski.net>,
       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>
Subject: Re: A few questions and issues with dynticks, NOHZ and powertop
References: <20100403223328.GA4507@comet.dominikbrodowski.net> <20100403235326.GA23445@core.coreip.homeip.net> <20100404104708.GA5922@comet.dominikbrodowski.net>
In-Reply-To: <20100404104708.GA5922@comet.dominikbrodowski.net>
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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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