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This article mainly explains "how to get ns nanosecond time in linux user space". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to get ns nanosecond time in linux user space".

I. introduction

When testing the performance of a program, we often need to obtain ns-level accurate time to measure the performance of a program. Here's how to get ns-level time in user space in linux.

Second, user space to obtain ns-level time

Using the clock_gettime function, the function prototype is as follows:

Long sys_clock_gettime (clockid_t which_clock, struct timespec * tp)

1.which_clock parameter interpretation

CLOCK_REALTIME: the real-time time of the system, which changes with the real-time time of the system, that is, starting from 0:0:0 in UTC1970-1-1. If the system time is supposed to be other by the user, the corresponding time will be changed accordingly.

CLOCK_MONOTONIC: timing starts from the moment the system starts, regardless of the change of the system time by the user

CLOCK_PROCESS_CPUTIME_ID: time spent from this process to the current code system CPU

CLOCK_THREAD_CPUTIME_ID: the time it takes from this thread to the current code system CPU

2.struct timespec structure

The code is as follows:

Struct timespec

{

Time_t tv_sec

Long int tv_nsec

}

The sample code for usage is as follows:

The code is as follows:

# include

# include

# include

Int main (void)

{

Struct timespec time_start= {0, 0}, time_end= {0, 0}

Clock_gettime (CLOCK_REALTIME, & time_start)

Printf ("start time% llus,%llu ns\ n", time_start.tv_sec, time_start.tv_nsec)

Clock_gettime (CLOCK_REALTIME, & time_end)

Printf ("endtime% llus,%llu ns\ n", time_end.tv_sec, time_end.tv_nsec)

Printf ("duration:%llus% lluns\ n", time_end.tv_sec-time_start.tv_sec, time_end.tv_nsec-time_start.tv_nsec)

Return 0

}

Compile command:

The code is as follows:

Gcc test.c-o test-lrt

Running result:

The code is as follows:

. / test

Start time 1397395863s,973618673 ns

Endtime 1397395863s,973633297 ns

Duration:0s 14624ns

From the running results, you can see that calling the printf () function requires about 15us at a time.

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