[Mesa-dev] [PATCH] i965: Compute VS attribute WA bits earlier and check if they changed.

[Kenneth Graunke]

On Thursday, December 04, 2014 03:13:59 PM Chris Forbes wrote:
> What's the perf impact on a platform which actually needs this?
> 
> I think there would be some further substantial gains to be had by
> giving this its own dirty bit -- piles of other atoms listen to
> BRW_NEW_VERTEX_PROGRAM, but don't care about the workaround bits.

Well...it looks like there are only 5:

gen6_sol_surfaces
brw_texture_surfaces
brw_vs_samplers
brw_vs_pull_constants
gen7_vs_state

The last two already listen to BRW_NEW_VS_PROG_DATA (CACHE_NEW_VS_PROG),
which is pretty much guaranteed to be flagged if you're switching WA bits.

gen6_sol_surfaces only happens on Gen6; I haven't measured perf there yet.

brw_texture_surfaces and brw_vs_samplers are definitely not necessary, but
also get flagged on BRW_NEW_BATCH.  The test I was measuring does lots of
small batches, so they pretty much happen all the time anyway.

So, at least on Haswell, using a separate dirty bit doesn't actually help
this benchmark much - I re-measured and got very similar numbers.

But you're right, three of those dependencies are totally unnecessary, and I
do hate adding bogus reasons to re-emit surfaces and sampler state.  I'm happy
to send a V2 that uses a separate dirty bit - it's a lot less confusing that
way, anyhow...

--Ken
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