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From: Peter Mutsaers <plm@xs4all.nl>
Subject: Re: gcc optimizations for kernel
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<8791ad5jed.fsf@plm.xs4all.nl> <n0E175F6A@longacre.demon.co.uk>
Date: Mon, 16 Sep 1996 05:44:32 GMT
>> On Sun, 15 Sep 1996 16:41:48 BST, searle@longacre.demon.co.uk
>> (Michael Searle) said:
>> Hmm, I've been running for months with a kernel compiled with
>> -O2, without problems. I assume that the sections of device
>> drivers that depend on order are not reordered by gcc, or the
>> makefiles force that -O2 not be used for such files.
MS> Well, so had I, but I've changed the Makefile to do -O on
MS> device drivers (there's a separate CFLAGS line). I tried to
MS> change it to do -O3 for the rest, but the result gave me the
MS> Black Screen of Death when starting X. (I think it was X that
MS> did it, it was certainly after login.)
I never tried -O3. Then -O2 must be safe, but -O3 not.
I would not use -O3 anyway since programs compiled with it tend to be
somewhat bigger than compiled with -O2 (loop-unroll
optimization?). For the kernel, occupying it's memory always, I'd
rather not have that. -O and -O2 make more difference than -O2 and -O3
wrt speed, so I would suggest to use -O2.
--
Peter Mutsaers | Abcoude (Utrecht),
plm@xs4all.nl | the Netherlands