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SubjectRe: [PATCH] Add option to build with -O3
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On Wed, Mar 5, 2014 at 6:37 AM, Jon Ringle <jringle@gridpoint.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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