On 1/17/06, Daniel Kristjansson <[EMAIL PROTECTED]> wrote: > On Mon, 2006-01-16 at 20:55 -0700, John P Poet wrote: > > Is there an easy way to configure Myth such that it builds with -Os > > instead of -O3? I have been editing the configure script before > > running it, but was wondering if there is a better way. > > > My frontend machine has a Intel Northwood 3.2GHz HT P4 and 512MB of > > RAM. With this configuration, I have found that compiling myth with > > -Os is better than -O3. > > Have you changed your compiler? > > The Northwood has a 512KB L2 cache, which should be sufficient for > -O2/-O3 to be faster than -Os. Generally the script is supposed to use > -Os for processors with 256 KB or smaller L2/L3 cache and -O2/-O3 for > ones with a 512KB or larger cache. The benchmarking I did for that > decision was with gcc 3.x. P4 based cores don't really need some > of the -O2/-O3 optimizations, like aligning jump targets, but some > of the newer processors like the Pentium-M and the Athlon chips do > benefit from the alignment; but they didn't seem to hurt with gcc 3.x. > > gcc 4+ does some additional optimization at -O2 and -O3 which may be > hurting you as far as cache performance is concerned. You might want > to try disabling the new optimizations in -02... > See http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gcc/Optimize-Options.html > And http://gcc.gnu.org/onlinedocs/gcc-3.3/gcc/Optimize-Options.html > > -- Daniel
Finally had some time to play with this. You are correct, I am using gcc-4. With gcc-4, -O2 produces better code for the frontend, than -O3 does. With -O2, playback at high bitrates and higher than 1.0x speeds is smoother than with -O3. John _______________________________________________ mythtv-dev mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-dev
