[Mesa-dev] [PATCH] radeonsi: add cs tracing v2

[Dave Airlie]

>
>>> correctly). But Marek is quite right that this only counts for state
>>> objects
>>> and makes no sense for set_* and draw_* calls (and I'm currently thinking
>>> how to avoid that and can't come up with a proper solution). Anyway it's
>>> definitely not an urgent problem for radeonsi.
>>
>> It will be a problem once we actually start caring about performance
>> and, most importantly, the CPU overhead of the driver.
>>
>>> I still think that writing into the command buffers directly (e.g.
>>> without
>>> wrapper functions) is a bad idea, cause that lead to mixing driver logic
>>> and
>>
>> I'm convinced the exact opposite is a bad idea, because it adds
>> another layer all commands must go through. A layer which brings no
>> advantage. Think about apps which issue 1k-10k draw calls per frame.
>> It's obvious that every byte moved around counts and the key to high
>> framerate is to do (almost) nothing in the driver. It looks like the
>> idea here is to make the driver as slow as possible.
>>
>>> packet building in r600g. For example just try to figure out how the
>>> relocation in NOPs work by reading the source (please keep in mind that
>>> one
>>> of the primary goals why AMD is supporting this driver is to give a good
>>> example code for customers who want to implement that stuff on their own
>>> systems).
>>
>> I'm shocked. Sacrificing performance in the name of making the code
>> nicer for some customers? Seriously? I thought the plan was to make
>> the best graphics driver ever.
>
>
> Well, maybe I'm repeating myself: Performance is not a priority, it's only
> nice to have!
>
> Sorry to say so, but if we sacrifice a bit of performance for more code
> readability than that is perfectly ok with me (Don't understand me wrong I
> would really prefer to replace the closed source driver today than tomorrow,
> it's unfortunately just not what I'm paid for).
>
> On the other hand, we are talking about perfectly optimizeable inline
> functions and/or macros. All I'm saying is that we should structurize the
> code a bit more.

Its okay to take steps in the right direction, but if you start taking
steps that away
from performance in lieu of code readability then please be prepared
to deal with
objections.

The thing is in a lot of cases, code readability is in the eye of the
beholder, I'm sure
Jerome though r600g was perfectly readable when he wrote it, but a lot
of us didn't
and spent a lot of time trying to remove the CPU overheads, not least
the amount of
time Marek spent. The thing is performance is measureable, code
readability isn't.

Dave.