linux-kernel - Re: [PATCH] Add option to build with -O3

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Message-ID: <CAFLxGvyB0r2RgeFhKoWqgWHLKEMF=BEM8ThRr8Mq6nGtJWQm1w@mail.gmail.com>
Date:	Thu, 6 Mar 2014 14:28:42 +0100
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Jon Ringle <jringle@...dpoint.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	"Ringle, Jonathan" <Jonathan.Ringle@...dpoint.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add option to build with -O3

On Wed, Mar 5, 2014 at 6:37 AM, Jon Ringle <jringle@...dpoint.com> wrote:
>
>
> On Wed, 5 Mar 2014, Greg KH wrote:
>
>> On Tue, Mar 04, 2014 at 07:01:49PM -0500, Jon Ringle wrote:
>> > +config CC_OPTIMIZE_FOR_SPEED
>> > +    bool "Optimze for speed (-O3)"
>> > +    help
>> > +      Enabling this option will pass "-O3" to gcc
>> > +      resulting in a larger kernel (but possibly faster)
>>
>> Are you sure about that?  Have you measured it?
>
> I do know that there is an improvement performance-wise for my particular
> use-case.
>
> My target is an ARM board being built with gcc-4.8.2. My board has on it a
> sc16is740 that is used as an RS-485 port. The sc16is740 is on the i2c bus,
> so when an interrupt comes in to indicate that there is data available to
> be read, I need to get the data over the i2c bus. I do this on a kthread
> to do this work. The i2c transactions (using i2c-davinci driver) are also
> interrupt driven. I was seeing a lot of lost packets when receiving data
> at only 19200. Adding the -O3 compile option helped in this regard in that
> I am now rarely seeing packet loss.

Please also see:
http://www.gossamer-threads.com/lists/linux/kernel/1835761?do=post_view_threaded#1835761

-- 
Thanks,
//richard
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