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/* Copyright 2023 Joshua Bakita
* Header-only library that provides an ultra-low-overhead GPU timing function,
* a copy monitoring kernel, and other useful sundries.
*/
#include <stdio.h>
#include <stdint.h>
// 4k pages (4096 bytes)
#define PG_SZ 0x1000
#define SAFE(x) \
if ((err = (cudaError_t)(x)) != 0) { \
printf("CUDA error %d! %s\n", err, cudaGetErrorString(err)); \
printf("Suspect line: %s\n", #x); \
exit(1); \
}
#define s2ns(s) ((s)*1000l*1000l*1000l)
#define ns2ms(s) ((s)/(1000l*1000l))
#define timediff(start, end) ((s2ns((end).tv_sec) + (end).tv_nsec) - (s2ns((start).tv_sec) + (start).tv_nsec))
// Compiles to 5 inline SASS instructions on sm_52
static __device__ inline uint64_t gclock64_fast(void) {
uint32_t lo_bits;
uint32_t hi_bits;
uint32_t hi_bits_2;
uint64_t ret;
// Upper bits may rollover between our first and 2nd read
asm volatile("mov.u32 %0, %%globaltimer_hi;" : "=r"(hi_bits));
asm volatile("mov.u32 %0, %%globaltimer_lo;" : "=r"(lo_bits));
asm volatile("mov.u32 %0, %%globaltimer_hi;" : "=r"(hi_bits_2));
// If upper bits rolled over, lo_bits = 0
lo_bits = (hi_bits != hi_bits_2) ? 0 : lo_bits;
// As sm_52 SASS is naively 32-bit, the following ops get optimized out
ret = hi_bits_2;
ret <<= 32;
ret |= lo_bits;
return ret;
}
/* Old copy function. Copyright Nathan Otterness
// Returns the value of CUDA's global nanosecond timer.
// Compiles to 9 inline SASS instructions on sm_52
static __device__ inline uint64_t gclock64(void) {
// Due to a bug in CUDA's 64-bit globaltimer, the lower 32 bits can wrap
// around after the upper bits have already been read. Work around this by
// reading the high bits a second time. Use the second value to detect a
// rollover, and set the lower bits of the 64-bit "timer reading" to 0, which
// would be valid, it's passed over during the duration of the reading. If no
// rollover occurred, just return the initial reading.
volatile uint64_t first_reading;
volatile uint32_t second_reading;
uint32_t high_bits_first;
asm volatile("mov.u64 %0, %%globaltimer;" : "=l"(first_reading));
high_bits_first = first_reading >> 32;
asm volatile("mov.u32 %0, %%globaltimer_hi;" : "=r"(second_reading));
if (high_bits_first == second_reading) {
return first_reading;
}
// Return the value with the updated high bits, but the low bits set to 0.
return ((uint64_t) second_reading) << 32;
}
*/
// This works by monitoring and recording when the last byte of each
// 4k page of the `devmem_to_watch` becomes non-zero.
// @param devmem_len Length of devmem_to_watch in bytes
// @param times Arr to store fin time of each pg cpy. Len == devmem_len / PG_SZ
__global__ void watch_devmem(char* devmem_to_watch, int devmem_len, uint64_t* times, int* barrier) {
volatile char* cursor = devmem_to_watch;
// If more than one thread is launched, distribute work by offsetting threads
if (blockDim.x > 1) {
times += threadIdx.x;
cursor += threadIdx.x * PG_SZ;
}
barrier[threadIdx.x] = 1;
// Assume they show up in the right order
while (cursor < devmem_to_watch + devmem_len) {
// Wait until last byte of the page is written to
while (!*(cursor + PG_SZ - 1))
continue;
*times = gclock64_fast(); // Log time
times += blockDim.x;
cursor += PG_SZ * blockDim.x; // Advance a page
}
}
static inline char* human_readable_bytes(size_t bytes) {
static char out[100];
if (bytes > 1024.*1024*1024)
snprintf(out, 100, "%.2fGiB", bytes/(1024.*1024*1024));
else if (bytes > 1024.*1024)
snprintf(out, 100, "%.2fMiB", bytes/(1024.*1024));
else if (bytes > 1024.)
snprintf(out, 100, "%.2fKiB", bytes/1024.);
return out;
}
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