<div dir="ltr"><div class="gmail_quote"><div dir="ltr">On Mon, Sep 17, 2018 at 8:34 AM Danylo Piliaiev <<a href="mailto:danylo.piliaiev@gmail.com">danylo.piliaiev@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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Hi Jason,<br>
<br>
I have implemented the extension and it works, however before
sending the patch I decided to see how it can interact with other
extension - VK_EXT_conditional_render<br>
and got confused:<br>
<br>
From the spec it is not disallowed to call functions of
VK_KHR_draw_indirect_count in conditional rendering block. So let's
say that predicate of conditional rendering<br>
will result in FALSE, we call <span class="m_8153322649885267684blob-code-inner m_8153322649885267684blob-code-marker-addition"><span class="m_8153322649885267684pl-s">vkCmdDrawIndirectCountKHR
which sees that there is already a predicate emitted and it
should be taken into account, since it will be FALSE<br>
all next predicates should result in FALSE. The issue is that I
don't see an easy way to do this.<br>
<br>
My current implementation uses the next predicate (it is same as
in GL implementation):<br>
<br>
<tt> /* While draw_index < maxDrawCount the predicate's
result will be</tt><tt><br>
</tt><tt> * (draw_index == maxDrawCount) ^ TRUE = TRUE</tt><tt><br>
</tt><tt> * When draw_index == maxDrawCount the result is</tt><tt><br>
</tt><tt> * (TRUE) ^ TRUE = FALSE</tt><tt><br>
</tt><tt> * After this all results will be:</tt><tt><br>
</tt><tt> * (FALSE) ^ FALSE = FALSE</tt><tt><br>
</tt><tt> */</tt><tt><br>
</tt><tt> anv_batch_emit(&cmd_buffer->batch,
GENX(MI_PREDICATE), mip) {</tt><tt><br>
</tt><tt> mip.LoadOperation = LOAD_LOAD;</tt><tt><br>
</tt><tt> mip.CombineOperation = COMBINE_XOR;</tt><tt><br>
</tt><tt> mip.CompareOperation = COMPARE_SRCS_EQUAL;</tt><tt><br>
</tt><tt> }</tt><br>
<br>
But if the initial predicate state is FALSE then when draw_index
equals maxDrawCount the result will be<br>
<tt>(FALSE) ^ TRUE = TRUE</tt><br>
Which isn't something we want. But without "not equal" operation
or without MI_MATH I don't see how to fix this.<br></span></span></div></blockquote><div><br></div><div>First off, thanks for looking into the combination of these two features. Getting them to work together nicely is half of the difficulty of these two extensions.<br></div><div><br></div><div>On platforms which support MI_MATH, I think we're probably better off just using it. For Ivy Bridge, the only thing I could think to do when both are in use would be to do two MI_PREDICATEs for every draw call. The first would be what you describe above and the second would be the MI_PREDICATE for the conditional render with COMBINE_AND. When the condition is true, the AND would have no effect and you would get the behavior above. If the condition is false, the above logic for implementing draw_indirect_count wouldn't matter because it would get ANDed with false. On Haswell and later, it's likely more efficient to just use MI_MATH and avoid re-loading the draw count and condition on every draw call. (We could just leave the draw count in CS_GPR0, for instance.) Does that work?</div><div><br></div><div>Since you're already looking at it, it may be best to implement the two extensions together as one patch series so we can be sure we have the interactions right. If we can't get them to play nicely together, we may have to disable one of them on Ivy Bridge and I'd rather not enable an extension and then take the functionality away later.<br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><span class="m_8153322649885267684blob-code-inner m_8153322649885267684blob-code-marker-addition"><span class="m_8153322649885267684pl-s">
I don't see anything related in Vulkan or GL specs neither I see
anything in Piglit and CTS tests.<br>
Maybe I'm missing something obvious, could you help me here?<br></span></span></div></blockquote><div><br></div><div>There's nothing preventing the two from being used together. If we don't have piglit tests that exercise the GL versions together, that would be bad. Have you found good Vulkan CTS tests for either of those two extensions? VK_KHR_indirect_count should have tests since it's a KHR extension but we may need to write the tests for EXT_conditional_render.</div><div><br></div><div>--Jason<br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div text="#000000" bgcolor="#FFFFFF"><span class="m_8153322649885267684blob-code-inner m_8153322649885267684blob-code-marker-addition"><span class="m_8153322649885267684pl-s">
You can find current implementation in <a href="https://gitlab.freedesktop.org/GL/mesa/commit/9d1c7ae0db618c6f7281d5f667c96612ff0bb2c2" target="_blank">https://gitlab.freedesktop.org/GL/mesa/commit/9d1c7ae0db618c6f7281d5f667c96612ff0bb2c2</a><br>
</span></span><tt></tt><br>
- Danil<br>
<br>
<div class="m_8153322649885267684moz-cite-prefix">On 9/12/18 6:30 PM, Danylo Piliaiev
wrote:<br>
</div>
<blockquote type="cite">
Hi, <br>
<br>
Thank you for the directions!<br>
<br>
<div class="m_8153322649885267684moz-cite-prefix">On 9/12/18 6:13 PM, Jason Ekstrand
wrote:<br>
</div>
<blockquote type="cite">
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<div>Danylo,</div>
<div><br>
</div>
<div>You're free to implement anything not already
implemented. Here are some other (probably simpler)
extensions that I think can be reasonably implemented on
Intel HW:</div>
</div>
</blockquote>
<blockquote type="cite">
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<div><br>
</div>
<div> - VK_EXT_conservative_rasterization</div>
<div> - VK_EXT_conditional_render</div>
</div>
</blockquote>
Didn't see them, will take closer look later.<br>
<blockquote type="cite">
<div dir="ltr">
<div><br>
</div>
<div>As far as VK_KHR_draw_indirect_count go, I haven't
implemented it yet because the "proper" implementation is
actually kind-of painful though not impossible. In general,
there are two ways it can be done:</div>
<div><br>
</div>
<div>## 1. The cheap and easy way</div>
<div><br>
</div>
<div>The spec explicitly allows for the cheap and easy way by
requiring the caller to pass in a maxDrawCount. The idea
here would be to emit maxDrawCount draw calls only have each
one of them predicated on draw_id <
draw_count_from_buffer. This one probably wouldn't take
much to wire up but it does mean doing maxDrawCount
3DPRIMITIVE commands no matter how many of them are actually
needed.</div>
</div>
</blockquote>
I saw such implementation for i965, looked straightforward and I
thought it will easily translate into Vulkan implementation.
Didn't know that it's possible to do it other way on Intel.<br>
<blockquote type="cite">
<div dir="ltr">
<div><br>
</div>
<div>## 2. The hard but maybe more correct way</div>
<div><br>
</div>
<div>The Intel command streamer does have the ability, if used
carefully, to loop. The difficulty here isn't in looping;
that can be done fairly easily on gen8+ by emitting a
predicated MI_BATCH_BUFFER_START that's predicated off of
the looping condition which jumps to the top of the loop.
The real difficult bit is taking your loop counter and using
it to indirectly access the array of draw information. In
order to do this, you have to have a self-modifying batch
buffer. In short, you would emit MI commands which read the
draw information into registers and also emit MI commands
(which would probably come before the first set) which write
the actual address into the location in the batch where the
first set of MI commands has their address to read from.
This would be a painful to debug mess of GPU hangs but could
actually be kind-of fun to implement.</div>
</div>
</blockquote>
The correct way looks interesting, I'll need some time to
understand details.<br>
<blockquote type="cite">
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<div><br>
</div>
<div>I hope I haven't scarred you away from working on anv; I
just wanted to make it clear what you're getting yourself
into. Both ways are totally implementable and I think you'd
pretty much have to do the first method on gen7 if we really
care about supporting it there. The second is totally
doable, it'll just involve some headaches when it's broken.
If you want to continue with this project after reading my
scarry e-mail, I recommend starting with method 1 to get
your feet wet and then we can look into method 2 once you
have that working.</div>
</div>
</blockquote>
I'll follow your recommendation and will start from the first
method.<br>
<br>
- Danil<br>
<blockquote type="cite">
<div dir="ltr">
<div><br>
</div>
<div>--Jason<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Wed, Sep 12, 2018 at 6:36 AM Danylo Piliaiev
<<a href="mailto:danylo.piliaiev@gmail.com" target="_blank">danylo.piliaiev@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello
everyone,<br>
<br>
I would like to try to implement one of the Vulkan
extensions - <br>
VK_KHR_draw_indirect_count for anv,<br>
unless someone is already working on it.<br>
<br>
It's a relatively minor extension and I saw that the same
functionality <br>
is already implemented<br>
for ARB_indirect_parameters in i965.<br>
<br>
Also I would appreciate any tips if there are any known
possible tricky <br>
parts.<br>
<br>
- Danil<br>
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</blockquote>
</div>
</blockquote>
<br>
</blockquote>
<br>
</div>
</blockquote></div></div>