On 11/05/2021 05:58, Dixit, Ashutosh wrote:
On Sun, 09 May 2021 16:11:43 -0700, Jason Ekstrand wrote:
Yes, landing GuC support may be the first step in removing execlist
support. The inevitable reality is that GPU scheduling is coming and
likely to be there only path in the not-too-distant future. (See also
the ongoing thread with AMD about fences.) I'm not going to pass
judgement on whether or not this is a good thing. I'm just reading the
winds and, in my view, this is where things are headed for good or ill.
In answer to the question above, the answer to "what do we gain from
GuC?" may soon be, "you get to use your GPU." We're not there yet and,
again, I'm not necessarily advocating for it, but that is likely where
things are headed.
A firmware-based submission model isn't a bad design IMO and, aside from
the firmware freedom issues, I think there are actual advantages to the
model. Immediately, it'll unlock a few features like parallel submission
(more on that in a bit) and long-running compute because they're
implemented in GuC and the work to implement them properly in the
execlist scheduler is highly non-trivial. Longer term, it may (no
guarantees) unlock some performance by getting the kernel out of the way.
I believe another main reason for GuC is support for HW based
virtualization like SRIOV. The only way to support SRIOV with execlists
would be to statically partition the GPU between VM's, any dynamic
partitioning needs something in HW.
FW-based command-submission is indeed a win for SRIOV and the current HW
architecture.
Thanks for chiming in!
Martin
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