Hello,
I've recently profiled the latency of LTTng tracepoints on arm platforms,
using the follow sample program:
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
static inline uint64_t get_time_nsec(void)
{
struct timespec ts;
if (caa_unlikely(clock_gettime(CLOCK_MONOTONIC, &ts))) {
ts.tv_sec = 0;
ts.tv_nsec = 0;
}
return ((uint64_t) ts.tv_sec * 1000000000ULL) + ts.tv_nsec;
}
int main(int argc, char *argv[])
{
unsigned int i;
int tp_num = 0;
uint64_t total_time = 0;
uint64_t now, nowz;
if (argc > 1) {
sscanf (argv[1],"%d",&tp_num);
}
for (i = 0; i < tp_num; i++) {
now = get_time_nsec();
lttng_ust_tracepoint(hello_world, my_first_tracepoint,
i, "some_str");
nowz = get_time_nsec();
total_time += (nowz - now);
}
if (tp_num) {
printf("---------------------------Average TP time is
%"PRIu64"---------------------------\n", total_time / tp_num);
}
}
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
I observed a big average latency variance on different platforms when tracing a
high number (many thousands to millions) of tracepoints:
* [platform 1] with CPU info running a linux kernel based on Buildroot
(4.19.273 aarch64 GNU/Linux):
BogoMIPS : 187.50
Features : fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd08
CPU revision : 3
* Saw an average latency of 2-3usec
* [platform 2] with CPU info running a linux kernel based on Amazon Linux
(4.14.294-220.533.amzn2.aarch64 aarch64 GNU/Linux):
BogoMIPS : 243.75
Features : fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp
asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x3
CPU part : 0xd0c
CPU revision : 1
* Saw an average latency of ~0.5usec
Are there any suggestions to root cause the high latency and potentially
improve it on platform 1?
Thanks and best regards,
Anas.
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