[Pixman] disable cache prefetch on ATOM can improve the gtkperf performance

[André Tupinambá]

Hi,

The prefetching instructions are very attached with the processor
cache architecture. Probably the ATOM processor has a very tiny cache
and this prefetching is dirtying the cache and forcing some others
loads from the main memory.

Disable all cache prefetch isn't a good idea, I think. But in some
functions (bit_fiill and memcpy, I guess) we use prefetching
instructions with 2 or 3 cache lines ahead. Maybe this code is
affecting the performance.

Unfortunately, I don't have access to any ATOM processor to make some test.

Regards,

André Tupinambá

On Wed, Jun 9, 2010 at 11:41 AM, Soeren Sandmann <sandmann at daimi.au.dk> wrote:
> Soeren Sandmann <sandmann at daimi.au.dk> writes:
>
>> prefetching. On an AMD Phenom with 512 KB of L2 and 512 KB of L3,
>> disabling prefetch was a tiny but consistent slow-down.
>
> Here are the numbers from the AMD:
>
> Existing code, with prefetching:
>
> [ # ]  backend                         test   min(s) median(s) stddev. count
> [  0]    image                    evolution   17.896   18.363   1.10%    6/6
> [  1]    image         firefox-planet-gnome   25.778   26.390   1.57%    6/6
> [  2]    image            firefox-talos-gfx   12.576   12.721   0.58%    6/6
> [  3]    image            firefox-talos-svg   60.303   61.098   0.53%    5/6
> [  4]    image         gnome-system-monitor    7.405    7.414   0.10%    6/6
> [  5]    image           gnome-terminal-vim    4.147    4.162   0.28%    6/6
> [  6]    image                         gvim   21.949   22.175   0.52%    6/6
> [  7]    image                midori-zoomed    5.656    5.714   0.70%    6/6
> [  8]    image                    ocitysmap    4.008    4.018   0.53%    6/6
> [  9]    image                      poppler    2.748    2.788   0.68%    6/6
> [ 10]    image           swfdec-giant-steps    2.717    2.736   0.48%    6/6
> [ 11]    image               swfdec-youtube    4.383    4.414   0.57%    6/6
> [ 12]    image            xfce4-terminal-a1    4.055    4.076   0.52%    6/6
>
> Without prefetching:
>
> [ # ]  backend                         test   min(s) median(s) stddev. count
> [  0]    image                    evolution   17.310   17.351   1.64%    6/6
> [  1]    image         firefox-planet-gnome   25.816   27.148   2.33%    6/6
> [  2]    image            firefox-talos-gfx   13.176   13.214   0.15%    6/6
> [  3]    image            firefox-talos-svg   61.269   61.319   0.08%    5/6
> [  4]    image         gnome-system-monitor    7.386    7.415   0.28%    6/6
> [  5]    image           gnome-terminal-vim    4.116    4.163   0.45%    6/6
> [  6]    image                         gvim   22.659   22.901   1.46%    6/6
> [  7]    image                midori-zoomed    5.713    5.714   0.03%    5/6
> [  8]    image                    ocitysmap    3.997    4.000   0.09%    6/6
> [  9]    image                      poppler    2.796    2.797   0.07%    5/6
> [ 10]    image           swfdec-giant-steps    2.741    2.754   0.20%    6/6
> [ 11]    image               swfdec-youtube    4.406    4.415   0.29%    6/6
> [ 12]    image            xfce4-terminal-a1    4.079    4.089   0.10%    6/6
>
> With prefetchnta prefetching:
>
> [ # ]  backend                         test   min(s) median(s) stddev. count
> [  0]    image                    evolution   18.041   18.166   0.29%    4/6
> [  1]    image         firefox-planet-gnome   27.042   27.149   0.15%    6/6
> [  2]    image            firefox-talos-gfx   13.216   13.255   0.15%    6/6
> [  3]    image            firefox-talos-svg   61.118   61.161   0.05%    5/6
> [  4]    image         gnome-system-monitor    7.399    7.412   0.14%    5/6
> [  5]    image           gnome-terminal-vim    4.170    4.178   0.14%    5/6
> [  6]    image                         gvim   20.473   22.519   4.43%    7/7
> [  7]    image                midori-zoomed    5.567    5.633   0.66%    6/6
> [  8]    image                    ocitysmap    4.005    4.012   0.16%    4/6
> [  9]    image                      poppler    2.771    2.795   0.78%    6/6
> [ 10]    image           swfdec-giant-steps    2.735    2.741   0.23%    6/6
> [ 11]    image               swfdec-youtube    4.385    4.394   0.42%    6/6
> [ 12]    image            xfce4-terminal-a1    4.060    4.091   0.31%    5/6
>
>
> Soren
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