linux-kernel - Re: [PATCH] lis3lv02d: provide means to disable polled input interface

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Message-ID: <alpine.LNX.2.00.1004091532150.8345@pobox.suse.cz>
Date:	Fri, 9 Apr 2010 15:32:59 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Éric Piel <eric.piel@...mplin-utc.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Samu Onkalo <samu.p.onkalo@...ia.com>,
	Pavel Machek <pavel@....cz>, lm-sensors@...sensors.org,
	linux-kernel@...r.kernel.org,
	Marcin Derlukiewicz <marcin@...lukiewicz.pl>
Subject: Re: [PATCH] lis3lv02d: provide means to disable polled input
 interface

On Fri, 9 Apr 2010, Éric Piel wrote:

> > This is reported to create 20% CPU usage increase (and proportionaly higher
> > power consumption) just for the ipolldevd kernel thread (which is used
> > to read the sensor).
> > 
> > As most users probably only use the freefall functionality of the driver
> > and not the joystick interface, provide means for disabling the registration
> > of joystick device altogether via module parameter.
> > (I'd rather make it default to 0, but this will break backwards compatibility).
> Are you saying there is a 20% CPU usage even when the joystick interface
> is not open? This should not happen (and this is not happening on my
> laptop). The polling should happen only when a userspace app opens the
> joystick interface (like running neverball).
> 
> So I'd tend to think it's more due to a misconfiguration of the system
> (like xserver using the joystick interface as a pointer device) or it's
> a bug in the way we set up the polling. Could you investigate and let me
> know?

Marcin originally reported this to me.

Marcin, could you please check 'lsof' output to see whether the joystick 
interface has been open by some application?

Thanks,

-- 
Jiri Kosina
SUSE Labs, Novell Inc.
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