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panfrost: Update scoreboarding notes

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Our understanding of the set/write value jobs has evolved, so let's
update the rules.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3836>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3836>
This commit is contained in:
Alyssa Rosenzweig 2020-02-16 13:58:09 -05:00
parent 88323d1ba0
commit 308f9cf104
1 changed files with 6 additions and 10 deletions
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16
src/gallium/drivers/panfrost/pan_scoreboard.c
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@ -49,7 +49,8 @@
*
* More specifically, here are a set of rules:
*
* - A set value job must appear if and only if there is at least one tiler job.
* - A write value job must appear if and only if there is at least one tiler
* job, and tiler jobs must depend on it.
*
* - Vertex jobs and tiler jobs are independent.
*
@ -57,8 +58,7 @@
* data from a vertex job, it depends on the vertex job. If it's getting data
* from software, this is null.
*
* - The first vertex job used as the input to tiling must depend on the set
* value job, if it is present.
* - Tiler jobs must depend on the write value job (chained or otherwise).
*
* - Tiler jobs must be strictly ordered. So each tiler job must depend on the
* previous job in the chain.
@ -70,9 +70,9 @@
*
* Justification for each rule:
*
* - Set value jobs set up tiling, essentially. If tiling occurs, they are
* needed; if it does not, we cannot emit them since then tiling partially
* occurs and it's bad.
* - Write value jobs are used to write a zero into a magic tiling field, which
* enables tiling to work. If tiling occurs, they are needed; if it does not,
* we cannot emit them since then tiling partially occurs and it's bad.
*
* - The hardware has no notion of a "vertex/tiler job" (at least not our
* hardware -- other revs have fused jobs, but --- crap, this just got even
@ -83,10 +83,6 @@
* read-before-write hazard. Tiler jobs get their data from vertex jobs, ergo
* tiler jobs depend on the corresponding vertex job (if it's there).
*
* - In fact, tiling depends on the set value job, but tiler jobs depend on the
* corresponding vertex jobs and each other, so this rule ensures each tiler
* job automatically depends on the set value job.
*
* - The tiler is not thread-safe; this dependency prevents race conditions
* between two different jobs trying to write to the tiler outputs at the
* same time.