82xx performance

[Rune Torgersen]

Arnd Bergmann wrote:
> On Tuesday 15 July 2008, Rune Torgersen wrote:
>> Using arch/ppc I got a 2.6.25 kernel to boot, and the kernel compile
>> test I did is almost identical (within 1%) of what the arch/powerpc
>> 2.6.25 did, so it seems to be a difference between 2.6.18 and 2.6.25
>> (I'll see if I can find an exact version, as I think my ppc port can
>> be compiled for all versions from 2.6.18 to 25)
> 
> You probably already know git-bisect, but if you don't, you should
> definitely give it a try. It's the best tool to find which patch
> exactly broke your performance.

Turns out the story is no so simple.
I redid the test wih all versions of arch/ppc from 2.6.18 to 2.6.26, and
also arch/powerpc (2.6.24 and 25, 26 doesn't compile because of binutil
issues)

This time I made very sure that the tests were performed the same way,
and I made a tabel showing relative performance:

kernel        compile time   rel   context switch  rel
v2.6.18         01:13:33.70  1.00       7.2        1.00
v2.6.19         01:13:29.21  1.00       7.1        0.99
v2.6.20         01:13:29.58  1.00       2.8        0.39
v2.6.21         01:13:24.91  1.00       8.1        1.13
v2.6.22         01:13:42.72  1.00       4.5        0.63
v2.6.23         01:15:16.43  1.02       17         2.36
v2.6.24         01:15:30.90  1.03       20         2.78
v2.6.25         01:14:51.21  1.02       21         2.92
v2.6.26         01:14:34.76  1.01       23.8       3.31
v2.6.24-powerpc 01:17:41.99  1.06       25.8       3.58
v2.6.25-powerpc 01:18:10.10  1.06       35.7       4.96

This shows that arch/ppc no matter versin is fairly consistent in speed.
Arch/powerpc is roughtly 6% worse.

The contect swith column is found running lat_ctx 2 from lmbench3, and
should be in microsecs.