Vc branch ready for testing

[Sven Langkamp]

On Tue, Sep 11, 2012 at 11:35 PM, JL VT <pentalis at gmail.com> wrote:

> On Tue, Sep 11, 2012 at 4:26 PM, Sven Langkamp <sven.langkamp at gmail.com>wrote:
>
>> On Tue, Sep 11, 2012 at 12:21 PM, JL VT <pentalis at gmail.com> wrote:
>>
>>> I have overclockable memory but I'm fairly sure we are not bottlenecked
>>> by memory, nowadays nearly nothing is.
>>>
>>> But I can still test, I can test at 1333 mhz and 1866 mhz (just an
>>> example) and see if there is a chance. Is there any other way to check for
>>> a memory bottleneck?
>>>
>> It's more like the oppsite. Most of the time the cpu is waiting for data.
>> Your RAM is much slower than the cache, cache misses are usually really
>> expensive.
>>
>> In the vc branch for example the masking for autobrush spends 2/3 of the
>> time doing memcpy. That's just copying the color into the dab.
>>
>
> Before purchasing my RAM I looked at a long list of benchmarks on Tom's
> hardware done on different types of software, and the only time the effect
> of faster RAM was really noticeable was on artificial benchmarks.
> Everywhere else, like games, encoding, video editing, it didn't go past 7%
> speedup, even going from 1333 Mhz to 2100 Mhz, or single to dual, or dual
> to quad channel. That's why I think it's not a memory problem. And if it
> was, maybe we can program things differently; after all, if other graphical
> software isn't affected by memory speed, why are we?.
>

That just shows that an existing program isn't going faster with faster
RAM. In both cases there program would do the same, just the memory access
is a little faster. In our case you have two version of the same algorithm
and one does more memory access than the other.

Beside the one expensive memcpy in the masking, I think it's not that bad
at the moment. Priority should still be vectorize the composite op.
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