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Date: Fri, 07 Mar 2014 07:39:53 -0500 From: Austin S Hemmelgarn <ahferroin7@...il.com> To: Richard Weinberger <richard.weinberger@...il.com>, 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 2014-03-06 08:28, Richard Weinberger wrote: > 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 > > Ironically, combining these might achieve a significant performance improvement over CONFIG_GENERIC_CPU and -O2. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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