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panfrost: Use canonical characterization of tls_size 

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7206>
This commit is contained in:
Alyssa Rosenzweig 2020-10-14 21:09:48 -04:00 committed by Marge Bot
parent a33827d3d3
commit e6152091ca
1 changed files with 4 additions and 26 deletions
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30
src/panfrost/lib/pan_scratch.c
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@ -57,39 +57,17 @@
* 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
* stack_size is logarithmic. Consider some sample values:
*
* stack size | log_stack_size
* ---------------------------
* 256 | 4
* 512 | 5
* 1024 | 6
*
* Noting that log2(256) = 8, we have the relation:
*
* 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), where s is
* positive:
*
* 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. If s=0, since
* there is no spilling used whatsoever, we may set log_stack_size to 0 to
* disable the stack.
* The size of Thread Local Storage is signaled to the GPU in the tls_size
* field, which has a log2 modifier and is in units of 16 bytes.
*/
/* Computes log_stack_size = ceil(log2(max(s, 16))) - 4 */
/* Computes log_stack_size = log2(ceil(s / 16)) */
unsigned
panfrost_get_stack_shift(unsigned stack_size)
{
if (stack_size)
return util_logbase2_ceil(MAX2(stack_size, 16)) - 4;
return util_logbase2(DIV_ROUND_UP(stack_size, 16));
else
return 0;
}