[libc-commits] [libc] [libc] Remove remaining GPU architecture dependent instructions (PR #81612)
Joseph Huber via libc-commits
libc-commits at lists.llvm.org
Tue Feb 13 07:13:58 PST 2024
https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/81612
Summary:
Recent patches have added solutions to the remaining sources of
divergence. This patch simply removes the last occures of things like
`has_builtin`, `ifdef` or builtins with feature requirements. The one
exception here is `nanosleep`, but I made changes in the
`__nvvm_reflect` pass to make usage like this actually work at O0.
Depends on https://github.com/llvm/llvm-project/pull/81331
>From 654806ca4e1fe9b903bcaa5c212a94c36a0cc885 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Tue, 13 Feb 2024 09:10:14 -0600
Subject: [PATCH] [libc] Remove remaining GPU architecture dependent
instructions
Summary:
Recent patches have added solutions to the remaining sources of
divergence. This patch simply removes the last occures of things like
`has_builtin`, `ifdef` or builtins with feature requirements. The one
exception here is `nanosleep`, but I made changes in the
`__nvvm_reflect` pass to make usage like this actually work at O0.
Depends on https://github.com/llvm/llvm-project/pull/81331
---
libc/src/__support/GPU/amdgpu/utils.h | 9 +--------
libc/src/__support/GPU/nvptx/utils.h | 6 ++----
libc/src/__support/RPC/rpc_util.h | 5 +++--
libc/src/time/gpu/nanosleep.cpp | 5 +++--
libc/src/time/gpu/time_utils.h | 20 +++++---------------
5 files changed, 14 insertions(+), 31 deletions(-)
diff --git a/libc/src/__support/GPU/amdgpu/utils.h b/libc/src/__support/GPU/amdgpu/utils.h
index 58bbe29cb3a7d7..6f704a262fbdf5 100644
--- a/libc/src/__support/GPU/amdgpu/utils.h
+++ b/libc/src/__support/GPU/amdgpu/utils.h
@@ -152,14 +152,7 @@ LIBC_INLINE uint64_t processor_clock() { return __builtin_readcyclecounter(); }
/// Returns a fixed-frequency timestamp. The actual frequency is dependent on
/// the card and can only be queried via the driver.
LIBC_INLINE uint64_t fixed_frequency_clock() {
- if constexpr (LIBC_HAS_BUILTIN(__builtin_amdgcn_s_sendmsg_rtnl))
- return __builtin_amdgcn_s_sendmsg_rtnl(0x83);
- else if constexpr (LIBC_HAS_BUILTIN(__builtin_amdgcn_s_memrealtime))
- return __builtin_amdgcn_s_memrealtime();
- else if constexpr (LIBC_HAS_BUILTIN(__builtin_amdgcn_s_memtime))
- return __builtin_amdgcn_s_memtime();
- else
- return 0;
+ return __builtin_readsteadycounter();
}
/// Terminates execution of the associated wavefront.
diff --git a/libc/src/__support/GPU/nvptx/utils.h b/libc/src/__support/GPU/nvptx/utils.h
index e7e297adf7ecca..5a31d7c140587f 100644
--- a/libc/src/__support/GPU/nvptx/utils.h
+++ b/libc/src/__support/GPU/nvptx/utils.h
@@ -138,13 +138,11 @@ LIBC_INLINE uint32_t get_lane_size() { return LANE_SIZE; }
}
/// Returns the current value of the GPU's processor clock.
-LIBC_INLINE uint64_t processor_clock() {
- return __nvvm_read_ptx_sreg_clock64();
-}
+LIBC_INLINE uint64_t processor_clock() { return __builtin_readcyclecounter(); }
/// Returns a global fixed-frequency timer at nanosecond frequency.
LIBC_INLINE uint64_t fixed_frequency_clock() {
- return __nvvm_read_ptx_sreg_globaltimer();
+ return __builtin_readsteadycounter();
}
/// Terminates execution of the calling thread.
diff --git a/libc/src/__support/RPC/rpc_util.h b/libc/src/__support/RPC/rpc_util.h
index ff9569298a1ed7..cc2a11a1108e01 100644
--- a/libc/src/__support/RPC/rpc_util.h
+++ b/libc/src/__support/RPC/rpc_util.h
@@ -21,8 +21,9 @@ namespace rpc {
/// Suspend the thread briefly to assist the thread scheduler during busy loops.
LIBC_INLINE void sleep_briefly() {
-#if defined(LIBC_TARGET_ARCH_IS_NVPTX) && __CUDA_ARCH__ >= 700
- __nvvm_nanosleep(64);
+#if defined(LIBC_TARGET_ARCH_IS_NVPTX)
+ if (__nvvm_reflect("__CUDA_ARCH") >= 700)
+ LIBC_INLINE_ASM("nanosleep.u32 64;" ::: "memory");
#elif defined(LIBC_TARGET_ARCH_IS_AMDGPU)
__builtin_amdgcn_s_sleep(2);
#elif defined(LIBC_TARGET_ARCH_IS_X86)
diff --git a/libc/src/time/gpu/nanosleep.cpp b/libc/src/time/gpu/nanosleep.cpp
index e84fe622100e80..5cf9e961e81256 100644
--- a/libc/src/time/gpu/nanosleep.cpp
+++ b/libc/src/time/gpu/nanosleep.cpp
@@ -22,14 +22,15 @@ LLVM_LIBC_FUNCTION(int, nanosleep,
uint64_t nsecs = req->tv_nsec + req->tv_sec * TICKS_PER_NS;
uint64_t start = gpu::fixed_frequency_clock();
-#if defined(LIBC_TARGET_ARCH_IS_NVPTX) && __CUDA_ARCH__ >= 700
+#if defined(LIBC_TARGET_ARCH_IS_NVPTX)
uint64_t end = start + nsecs / (TICKS_PER_NS / GPU_CLOCKS_PER_SEC);
uint64_t cur = gpu::fixed_frequency_clock();
// The NVPTX architecture supports sleeping and guaruntees the actual time
// slept will be somewhere between zero and twice the requested amount. Here
// we will sleep again if we undershot the time.
while (cur < end) {
- __nvvm_nanosleep(static_cast<uint32_t>(nsecs));
+ if (__nvvm_reflect("__CUDA_ARCH") >= 700)
+ LIBC_INLINE_ASM("nanosleep.u32 %0;" ::"r"(nsecs));
cur = gpu::fixed_frequency_clock();
nsecs -= nsecs > cur - start ? cur - start : 0;
}
diff --git a/libc/src/time/gpu/time_utils.h b/libc/src/time/gpu/time_utils.h
index 531a748665b07b..b1edbbb387b37b 100644
--- a/libc/src/time/gpu/time_utils.h
+++ b/libc/src/time/gpu/time_utils.h
@@ -15,24 +15,14 @@ namespace LIBC_NAMESPACE {
#if defined(LIBC_TARGET_ARCH_IS_AMDGPU)
// AMDGPU does not have a single set frequency. Different architectures and
-// cards can have vary values. Here we default to a few known values, but for
-// complete support the frequency needs to be read from the kernel driver.
-#if defined(__GFX10__) || defined(__GFX11__) || defined(__GFX12__) || \
- defined(__gfx940__) || defined(__gfx941__) || defined(__gfx942__)
-// These architectures use a 100 MHz fixed frequency clock.
-constexpr uint64_t clock_freq = 100000000;
-#elif defined(__GFX9__)
-// These architectures use a 25 MHz fixed frequency clock expect for Vega 10
-// which is actually 27 Mhz. We default to 25 MHz in all cases anyway.
-constexpr uint64_t clock_freq = 25000000;
-#else
-// The frequency for these architecture is unknown. We simply default to zero.
-constexpr uint64_t clock_freq = 0;
+// cards can have different values. The actualy frequency needs to be read from
+// the kernel driver and will be between 25 MHz and 100 MHz on most cards. All
+// cards following the GFX9 ISAs use a 100 MHz clock so we will default to that.
+constexpr uint64_t clock_freq = 100000000UL;
#endif
// We provide an externally visible symbol such that the runtime can set
-// this to the correct value. If it is not set we try to default to the
-// known values.
+// this to the correct value.
extern "C" [[gnu::visibility("protected")]] uint64_t
[[clang::address_space(4)]] __llvm_libc_clock_freq;
#define GPU_CLOCKS_PER_SEC static_cast<clock_t>(__llvm_libc_clock_freq)
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