Messages in this thread | | | Date | Wed, 31 Mar 1999 13:52:50 -0500 | From | Arvind Sankar <> | Subject | Re: Linux-2.2.5 - and a vacation |
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On Wed, Mar 31, 1999 at 12:54:38PM -0600, Brandon Black wrote: > Arvind Sankar wrote: > > > On Tue, Mar 30, 1999 at 02:42:55PM -0600, Brandon Black wrote: > > > I'm actually way past taking my life in my own hands, in that the > > > binutils, compiler, and kernel have all been built using egcs-1.1.2 with > > > the following optimization flags: > > > > > > -march=pentiumpro -O6 -fomit-frame-pointer -malign-loops=0 > > > -malign-functions=0 -malign-jumps=0 > > > (yes, even the kernel at O6). > > > > well, if you have a pentiumpro, that should really be > > -malign-loops=4 etc. You might also try adding -funroll-loops. > > > > I wonder if -fno-strict-aliasing might be better for the kernel? > > > > btw, egcs doesn't really have -O levels beyond 3. > > > > -- arvind > > hmmm... I've tried -fstrcit-aliasing and -fno-strict-aliasing, and I can't > see any notable difference, but I don't have any way of qualitatively > profiling the kernel's performance, they both compile and work though.
I figure the kernel will do weird things which screw up -fstrict-aliasing, so its for correctness, not speed.
> > About alignment.... the info I have found was that pentiums like -malign-*=2, > and PPro's supposedly liked either 2 or 4 depending on who you ask, and then > I read somewhere else that PII (at least the latest Deschutes ones) and later > processors should go back to 0, because for some reason the alignment didn't > help them much, and removing the padding would save space in the L2 (and to a > small degree the L1) cache.... so that's why I went with zero. Do you (or > anybody on the list) no for sure the optimal alignment for the PII Deschutes?
Hm. I think I read somewhere on Intel's page (some doc about optimizing for pentium class cpus) that p2 likes alignment on 16-byte boundaries. Will check again later.
> > I kind-of assumed since gcc (I think) does thigns at least to 6, and so does > pgcc, both of which go into egcs, that egcs would have an O6... oh well :)
oh, gcc does too? that's weird...
-- arvind
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