From: Dexuan Cui <decui@microsoft.com>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
CC: Dan Carpenter <dan.carpenter@oracle.com>,
        "linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        "driverdev-devel@linuxdriverproject.org" 
	<driverdev-devel@linuxdriverproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "tomi.valkeinen@ti.com" <tomi.valkeinen@ti.com>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "apw@canonical.com" <apw@canonical.com>,
        "plagnioj@jcrosoft.com" <plagnioj@jcrosoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>
Subject: RE: [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen by
 force on VM panic
Thread-Topic: [PATCH v2] video: hyperv: hyperv_fb: refresh the VM screen by
 force on VM panic
Thread-Index: AQHPmo7K9bmiR/mw30qA8kPuB/vMKpuWvrIAgAAFu4CAADUD0A==
Date: Wed, 9 Jul 2014 01:46:18 +0000
Message-ID: <EE124450C0AAF944A40DD71E61F878C987AEB9@SINEX14MBXC417.southpacific.corp.microsoft.com>
References: <1403818501-15547-1-git-send-email-decui@microsoft.com>
 <20140708092709.GI25880@mwanda>
 <EE124450C0AAF944A40DD71E61F878C987A663@SINEX14MBXC417.southpacific.corp.microsoft.com>
 <20140708223425.GB6310@kroah.com>
In-Reply-To: <20140708223425.GB6310@kroah.com>
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Sender: linux-kernel-owner@vger.kernel.org

> -----Original Message-----
> > > From: Dan Carpenter [mailto:dan.carpenter@oracle.com]
> > > Sent: Tuesday, July 8, 2014 17:27 PM
> > > To: Dexuan Cui
> > > Cc: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org;
> driverdev-
> > > devel@linuxdriverproject.org; plagnioj@jcrosoft.com;
> > > tomi.valkeinen@ti.com; linux-fbdev@vger.kernel.org; olaf@aepfle.de;
> > > apw@canonical.com; jasowang@redhat.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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