Re: [PATCH v2 01/24] input: Add ff-memless-next module

From: Oliver Neukum <oneukum@suse.de>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: "Michal Malý" <madcatxster@devoid-pointer.net>,
	linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
	jkosina@suse.cz, elias.vds@gmail.com, anssi.hannula@iki.fi,
	simon@mungewell.org
Subject: Re: [PATCH v2 01/24] input: Add ff-memless-next module
Date: Wed, 23 Apr 2014 19:06:08 +0200	[thread overview]
Message-ID: <1398272768.23603.1.camel@linux-fkkt.site> (raw)
In-Reply-To: <20140423155923.GB10531@core.coreip.homeip.net>

On Wed, 2014-04-23 at 08:59 -0700, Dmitry Torokhov wrote:
> On Wed, Apr 23, 2014 at 02:12:59PM +0200, Oliver Neukum wrote:
> > On Tue, 2014-04-22 at 15:59 +0200, Michal Malý wrote:
> > > +/* Some devices might have a limit on how many uncombinable effects
> > > + * can be played at once */
> > > +static int mlnx_upload_conditional(struct mlnx_device *mlnxdev,
> > > +                                  const struct ff_effect *effect)
> > > +{
> > > +       struct mlnx_effect_command ecmd = {
> > > +               .cmd = MLNX_UPLOAD_UNCOMB,
> > > +               .u.uncomb.id = effect->id,
> > > +               .u.uncomb.effect = effect
> > > +       };
> > > +       return mlnxdev->control_effect(mlnxdev->dev, mlnxdev->private,
> > > &ecmd);
> > > +}
> > > +
> > 
> > This mean you are building the structure on the stack
> > 
> > 1. Are you sure nobody retains a reference?
> > 2. That is needlessly inefficient
> 
> Why is it inefficient?

The compiler has to include the data structure and then make
a memcopy to the stack. Instead a pointer to the predined structure
could be passed.

	Regards
		Oliver