Re: Locking comment on shrink_caches()

George Greer
2001-09-26T19:04:02Z

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