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b41692caf4
If stack isn't used, don't allocate it - simple as that. 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/6373>
109 lines
4.6 KiB
C
109 lines
4.6 KiB
C
/*
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* Copyright (C) 2019 Collabora, Ltd.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* Authors:
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* Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
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*/
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#include "util/u_math.h"
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#include "util/macros.h"
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#include "pan_encoder.h"
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/* Midgard has a small register file, so shaders with high register pressure
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* need to spill from the register file onto the stack. In addition to
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* spilling, it is desireable to allocate temporary arrays on the stack (for
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* instance because the register file does not support indirect access but the
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* stack does).
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*
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* The stack is located in "Thread Local Storage", sometimes abbreviated TLS in
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* the kernel source code. Thread local storage is allocated per-thread,
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* per-core, so threads executing concurrently do not interfere with each
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* other's stacks. On modern kernels, we may query
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* DRM_PANFROST_PARAM_THREAD_TLS_ALLOC for the number of threads per core we
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* must allocate for, and DRM_PANFROST_PARAM_SHADER_PRESENT for a bitmask of
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* shader cores (so take a popcount of that mask for the number of shader
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* cores). On older kernels that do not support querying these values,
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* following kbase, we may use the worst-case value of 256 threads for
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* THREAD_TLS_ALLOC, and the worst-case value of 16 cores for Midgard per the
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* "shader core count" column of the implementations table in
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* https://en.wikipedia.org/wiki/Mali_%28GPU% [citation needed]
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*
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* Within a particular thread, there is stack allocated. If it is present, its
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* size is a power-of-two, and it is at least 16 bytes. Stack is allocated
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* with the shared memory descriptor used for all shaders within a frame (note
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* that they don't execute concurrently so it's fine). So, consider the maximum
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* stack size used by any shader within a job, and then compute (where npot
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* denotes the next power of two):
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*
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* bytes/thread = npot(max(size, 16))
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* allocated = (# of bytes/thread) * (# of threads/core) * (# of cores)
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*
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* The size of Thread Local Storage is signaled to the GPU in a dedicated
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* log_stack_size field. Since stack sizes are powers of two, it follows that
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* stack_size is logarithmic. Consider some sample values:
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*
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* stack size | log_stack_size
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* ---------------------------
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* 256 | 4
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* 512 | 5
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* 1024 | 6
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*
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* Noting that log2(256) = 8, we have the relation:
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*
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* stack_size <= 2^(log_stack_size + 4)
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*
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* Given the constraints about powers-of-two and the minimum of 256, we thus
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* derive a formula for log_stack_size in terms of stack size (s), where s is
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* positive:
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*
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* log_stack_size = ceil(log2(max(s, 16))) - 4
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*
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* There are other valid characterisations of this formula, of course, but this
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* is computationally simple, so good enough for our purposes. If s=0, since
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* there is no spilling used whatsoever, we may set log_stack_size to 0 to
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* disable the stack.
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*/
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/* Computes log_stack_size = ceil(log2(max(s, 16))) - 4 */
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unsigned
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panfrost_get_stack_shift(unsigned stack_size)
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{
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if (stack_size)
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return util_logbase2_ceil(MAX2(stack_size, 16)) - 4;
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else
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return 0;
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}
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/* Computes the aligned stack size given the shift and thread count. */
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unsigned
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panfrost_get_total_stack_size(
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unsigned thread_size,
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unsigned threads_per_core,
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unsigned core_count)
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{
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unsigned size_per_thread = (thread_size == 0) ? 0 :
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util_next_power_of_two(ALIGN_POT(thread_size, 16));
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return size_per_thread * threads_per_core * core_count;
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}
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