[Mesa-dev] [PATCH] panfrost: Use tiler fast path (performance boost)

[Connor Abbott]

On Thu, Feb 21, 2019 at 5:07 PM Alyssa Rosenzweig <alyssa at rosenzweig.io>
wrote:

> > Yes, there is a buffer for holding the results of the tiler. The way it
> > works is that the userspace driver allocates a very large buffer with a
> > "grow on page fault" bit, so the kernel will allocate more memory as the
> > tiler asks for it.
>
> To be clear, right now I have this magic misc_0 buffer setup that way,
> too (allocating something enormous and setting GROW_ON_GPF). Although,
> it's not clear to me that that is the _correct_ thing to do; IIRC, the
> blob allocates "just enough", no GROW_ON_GPF needed, but I should
> probably check that.
>

I don't know about Midgard, but on Bifrost it definitely uses GROW_ON_GPF,
telling the kernel to preallocate some small-ish initial set, presumably as
an optimization. I don't think you can accurately predict how much memory
you're going to need ahead of time, since it depends on how the triangles
are distributed along the screen.
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