linux-kernel - RE: [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen by force on VM panic

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Date:	Wed, 9 Jul 2014 01:46:18 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:	Dan Carpenter <dan.carpenter@...cle.com>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tomi.valkeinen@...com" <tomi.valkeinen@...com>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"plagnioj@...osoft.com" <plagnioj@...osoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen by
 force on VM panic

> -----Original Message-----
> > > From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> > > Sent: Tuesday, July 8, 2014 17:27 PM
> > > To: Dexuan Cui
> > > Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> driverdev-
> > > devel@...uxdriverproject.org; plagnioj@...osoft.com;
> > > tomi.valkeinen@...com; linux-fbdev@...r.kernel.org; olaf@...fle.de;
> > > apw@...onical.com; jasowang@...hat.com; Haiyang Zhang
> > > Subject: Re: [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen
> by
> > > force on VM panic
> > >
> > > Don't use likely/unlikely unless you have benchmark numbers to show
> that
> > > it makes a speed up.
> > >
> > > regards,
> > > dan carpenter
> >
> > Hi Dan,
> > Here the variable 'synchronous_fb' is only set to true when the system
> panics.
> > So before the system panics, it's always 'unlikely'. :-)
> 
> Then take advantage of gcc's and your processor's prediction, which
> knows that 0 is the "common" case and will choose to do the right thing
> here.
> 
> Dan is right, never put those markings in your code unless you can
> benchmark the difference.  Which means in reality, never put them in
> your code.
> 
> gerg k-h

OK, let me send out a v3 patch, which will remove the unlikely.

Thanks,
-- Dexuan
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