[Mesa-dev] [PATCH 3/3] mesa: don't check mapped buffers in every draw call if drivers allow it

[Thomas Helland]

2017-05-16 1:05 GMT+02:00 Marek Olšák <maraeo at gmail.com>:
> On Tue, May 16, 2017 at 12:21 AM, Thomas Helland
> <thomashelland90 at gmail.com> wrote:
>> 2017-05-15 21:08 GMT+00:00 Marek Olšák <maraeo at gmail.com>:
>>> On Mon, May 15, 2017 at 10:00 PM, Thomas Helland
>>> <thomashelland90 at gmail.com> wrote:
>>>> Would this be a win for a game limited by the winsys/buffer handling?
>>>> I played some Hitman the other day, and noticed my gpu-utilization
>>>> was hovering at about 80%. Some profiling later and I concluded
>>>> that one thread was pegged at 100% doing buffer handling work.
>>>> amdgpu_cs_add_buffer, amdgpu_lookup_buffer, the cso_hash,
>>>> and a couple other functions related to the winsys where the hottest.
>>>> Should I expect that to be mitigated by your threaded_gallium work,
>>>> or by this patch series? If so, I will not delve into that much further =)
>>>
>>> amdgpu_cs_add_buffer and amdgpu_lookup_buffer overhead will definitely
>>> be hidden by threaded gallium. cso_hash will not.
>>>
>>> I don't think what you're seeing is related, but I'd be interested in
>>> a screenshot of sysprof showing what you described.
>>>
>>> Marek
>>
>> The below dropbox link has two screenshots showing the situation.
>> The data was collected by attaching perf to the process,
>> and the report was made with "perf report --hierarchy".
>> I can collect data with sysprof on Thursday, if you want.
>> My cpu(FX8320) was hovering at about 50% load at the time,
>> so with one of eight cores being pegged at 100% that matches
>> pretty well up with the 24% we're seeing here.
>> (25% * 50% = 12.5% = 1/8).
>> As can be seen from the second screenshots the overhead
>> is quite evently distributed, with no one function being the big offender.
>> However, what I noticed was amdgpu_cs_add_buffer,
>> si_set_constant_buffer and amdgpu_lookup_buffer.
>> I might be completely of track though, so you should
>> probably take this with the usual tablespoon of salt.
>>
>> https://www.dropbox.com/sh/r815zuklfwxy20q/AABrtKkb6Dc4pnW4u5Ul86-Ua?dl=0
>
> I think the problem is that you don't build Mesa with
> -fno-omit-frame-pointer, so frame-pointer-based profiling doesn't show
> the total time spent in functions and doesn't show call trees either.
>
> To demonstrate what sysprof should look like, this is DrawElements
> (main app thread):
> https://people.freedesktop.org/~mareko/sysprof_DrawElements.png
>
> This is the basic look at the gallium thread:
> https://people.freedesktop.org/~mareko/sysprof_gallium_threaded.png
>
> And this is the CS ioctl thread. Note that the call tree goes all the
> way to the kernel driver:
> https://people.freedesktop.org/~mareko/sysprof_cs_thread.png
>
> Marek

Hmm...

It might be that I'm somehow misrepresenting the data.
I'm quite confident I built with no-omit-frame-pointer though,
as I specifically spent a good amount of time figuring out how
to add the correct compile flags to the build without enabling
other debugging functions. But I might have messed up something.
I'll look into this a bit closer when I find the time, but that likely
won't be until Thursday as the very earliest.

Thanks for the help, it's always appreciated!