[Bugfix][Kernel] Implement acquire/release polyfill for Pascal (vllm-project#8776)

Signed-off-by: Amit Garg <mitgarg17495@gmail.com>

Author: sasha0552

csrc/custom_all_reduce.cuh

@@ -131,15 +131,26 @@ DINLINE O downcast(array_t<float, O::size> val) {
 }
 
 static DINLINE void st_flag_release(FlagType* flag_addr, FlagType flag) {
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 700
   asm volatile("st.release.sys.global.u32 [%1], %0;" ::"r"(flag),
                "l"(flag_addr));
+#else
+  asm volatile("membar.sys; st.volatile.global.u32 [%1], %0;" ::"r"(flag),
+               "l"(flag_addr));
+#endif
 }
 
 static DINLINE FlagType ld_flag_acquire(FlagType* flag_addr) {
   FlagType flag;
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 700
   asm volatile("ld.acquire.sys.global.u32 %0, [%1];"
                : "=r"(flag)
                : "l"(flag_addr));
+#else
+  asm volatile("ld.volatile.global.u32 %0, [%1]; membar.gl;"
+               : "=r"(flag)
+               : "l"(flag_addr));
+#endif
   return flag;
 }
 

csrc/custom_all_reduce_test.cu

@@ -44,7 +44,14 @@
   } while (0)
 
 __global__ void dummy_kernel() {
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 700
   for (int i = 0; i < 100; i++) __nanosleep(1000000);  // 100ms
+#else
+  for (int i = 0; i < 100; i++) {
+    long long int start = clock64();
+    while (clock64() - start < 150000000);  // approximately 98.4ms on P40
+  }
+#endif
 }
 
 template <typename T>