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panfrost: Simplify stack shift calculation

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I'm not sure why I never saw smaller values, but here you go.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3950>
This commit is contained in:
Alyssa Rosenzweig
2020-02-25 15:40:20 -05:00
committed by Tomeu Vizoso
parent 40fd1f9da4
commit 2fea44c636
1 changed files with 14 additions and 7 deletions
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src/panfrost/encoder/pan_scratch.c
+14 -7
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@@ -47,13 +47,14 @@
* https://en.wikipedia.org/wiki/Mali_%28GPU% [citation needed]
*
* Within a particular thread, there is stack allocated. If it is present, its
* size is a power-of-two, and it is at least 256 bytes. Stack is allocated
* size is a power-of-two, and it is at least 16 bytes. Stack is allocated
* with the shared memory descriptor used for all shaders within a frame (note
* that they don't execute concurrently so it's fine). So, consider the maximum
* stack size used by any shader within a job, and then compute (where npot
* denotes the next power of two):
*
* allocated = npot(max(size, 256)) * (# of threads/core) * (# of cores)
* bytes/thread = npot(max(size, 16))
* allocated = (# of bytes/thread) * (# of threads/core) * (# of cores)
*
* The size of Thread Local Storage is signaled to the GPU in a dedicated
* log_stack_size field. Since stack sizes are powers of two, it follows that
@@ -70,20 +71,26 @@
* stack_size <= 2^(log_stack_size + 4)
*
* Given the constraints about powers-of-two and the minimum of 256, we thus
* derive a formula for log_stack_size in terms of stack size (s):
* derive a formula for log_stack_size in terms of stack size (s), where s is
* positive:
*
* log_stack_size = ceil(log2(max(s, 256))) - 4
* log_stack_size = ceil(log2(max(s, 16))) - 4
*
* There are other valid characterisations of this formula, of course, but this
* is computationally simple, so good enough for our purposes.
* is computationally simple, so good enough for our purposes. If s=0, since
* there is no spilling used whatsoever, we may set log_stack_size to 0 to
* disable the stack.
*/
/* Computes log_stack_size = ceil(log2(max(s, 256))) - 4 */
/* Computes log_stack_size = ceil(log2(max(s, 16))) - 4 */
unsigned
panfrost_get_stack_shift(unsigned stack_size)
{
return util_logbase2_ceil(MAX2(stack_size, 256)) - 4;
if (stack_size)
return util_logbase2_ceil(MAX2(stack_size, 16)) - 4;
else
return 0;
}
/* Computes the aligned stack size given the shift and thread count. The blob