Messages in this thread |  | | Date | Wed, 26 Sep 2001 15:04:06 -0400 (EDT) | From | George Greer <> | Subject | Re: Locking comment on shrink_caches() |
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On Wed, 26 Sep 2001, Linus Torvalds wrote:
> >On Wed, 26 Sep 2001, Dave Jones wrote: >> On Wed, 26 Sep 2001, Alan Cox wrote: >> >> > VIA Cyrix CIII (original generation 0.18u) >> > >> > nothing: 28 cycles >> > locked add: 29 cycles >> > cpuid: 72 cycles >> >> Interesting. From a newer C3.. >> >> nothing: 30 cycles >> locked add: 31 cycles >> cpuid: 79 cycles >> >> Only slightly worse, but I'd not expected this. > >That difference can easily be explained by the compiler and options. > >You should use "gcc -O2" at least, in order to avoid having gcc do >unnecessary spills to memory in between the timings. And there may be some >versions of gcc that en dup spilling even then.
Nice big difference in 'locked add' seen here.
gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-85) 2x Pentium 233/MMX
-O0 -O2 nothing: 15 cycles nothing: 14 cycles locked add: 60 cycles locked add: 32 cycles cpuid: 33 cycles cpuid: 32 cycles
gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-85) 2x Pentium 133
-O0 -O2 nothing: 14 cycles nothing: 13 cycles locked add: 76 cycles locked add: 25 cycles cpuid: 31 cycles cpuid: 30 cycles
-- George Greer, greerga@m-l.org | Genius may have its limitations, but stupidity http://www.m-l.org/~greerga/ | is not thus handicapped. -- Elbert Hubbard
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