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

[Jerome Glisse]

On Tue, Mar 26, 2013 at 6:45 PM, Dave Airlie <airlied at gmail.com> wrote:
>>
>>>> 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.

Maybe once again you forgot why i did things the way i did them, i
explained myself to you back then, i designed r600g for a new kernel
api which was violently different from the cs one, my hope was that
the other kernel api would be better, it was not and i never pushed
more on that front. So r600g design was definitely not adapted to the
cs ioctl and not thinked for it. History often explain a lot of things
and people seems to forget about them.

That being said, i too find ironic the code readability argument, if
one understand the cs ioctl then the r600g code as it's nowadays make
sense, but the radeonsi code is closer to what r600g use to be. So
assuming same ioctl i would say that radeonsi should move towards what
r600g is nowadays.

Anyway just wanted to set history straight.

Cheers,
Jerome