linux-kernel - Re: Re: [PATCH v4 11/18] input: Add initial support for TWL6040 vibrator

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Date:	Mon, 13 Jun 2011 14:20:28 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Péter Ujfalusi <peter.ujfalusi@...com>,
	Tejun Heo <tj@...nel.org>
Cc:	"Girdwood, Liam" <lrg@...com>, Tony Lindgren <tony@...mide.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"Lopez Cruz, Misael" <misael.lopez@...com>,
	Jorge Eduardo Candelaria <jorge.candelaria@...com>
Subject: Re: Re: [PATCH v4 11/18] input: Add initial support for TWL6040
 vibrator

On Mon, Jun 13, 2011 at 12:51:16PM +0300, Péter Ujfalusi wrote:
> On Sunday 12 June 2011 01:18:54 Dmitry Torokhov wrote:
> 
> > > +static int twl6040_vibra_open(struct input_dev *input)
> > > +{
> > > +     struct vibra_info *info = input_get_drvdata(input);
> > > +
> > > +     info->workqueue = create_singlethread_workqueue("vibra");
> > > +     if (info->workqueue == NULL) {
> > > +             dev_err(&input->dev, "couldn't create workqueue\n");
> > > +             return -ENOMEM;
> > > +     }
> > 
> > Why do we need to create a separate workqueue? With arrival of CWQ
> > it looks like we should be able to use one of the system-wide
> > workqueues for this.
> 
> The reason for this is to ensure that we have the lowest latency as possible 
> in most case. In the embedded devices we use the vibra for tactile type of 
> feedbacks as well, where few tens of ms delay can be felt.

Even if you create a dedicated workqueue with CWQ it will still be using
shared pool of threads so I do not think that latency will be affected
by using system-wide workqueue. I might be mistaken though, Tejun will
correct me if I am wrong...

Thanks.

-- 
Dmitry
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