On 2014-03-06 08:28, Richard Weinberger wrote:
> On Wed, Mar 5, 2014 at 6:37 AM, Jon Ringle <jrin...@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
>
>
Ironically, combining these might achieve a significant performance
improvement over CONFIG_GENERIC_CPU and -O2.
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