Messages in this thread | | | Date | Mon, 25 Jun 2007 02:41:06 +0200 | From | Adrian Bunk <> | Subject | -Os versus -O2 |
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On Sun, Jun 24, 2007 at 05:23:42PM -0700, Arjan van de Ven wrote: > On Sun, 2007-06-24 at 20:12 -0400, Benjamin LaHaise wrote: > > On Sun, Jun 24, 2007 at 05:09:16PM -0700, Arjan van de Ven wrote: > > > if you care about the last cycle, don't specify -Os but -O2. > > > simple as that... you get what you tell the compiler you want. > > > > Certain distros are shipping kernels compiled with -Os. And it's more > > than just a couple of cycles. > > so those distros pick space over some cycles. Who are you to then > override that choice ? ;-) > > seriously, why are we even talking about overriding a choice the user > (or distro vendor as user) made here?
There is a real issue in the fact that compiling with -Os is available through a kconfig option and AFAIR used by some distributions.
I doubt distros enable CONFIG_CC_OPTIMIZE_FOR_SIZE due to size considerations, but due to speed considerations.
I wouldn't care if CONFIG_CC_OPTIMIZE_FOR_SIZE was hidden behind CONFIG_EMBEDDED, but as long as it's available as a general purpose option we have to consider it's performance.
The interesting questions are: Does -Os still sometimes generate faster code with gcc 4.2? If yes, why?
cu Adrian
--
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