3.2. MRG Realtime Specific gettimeofday speedup

3.2. MRG Realtime Specific `gettimeofday` speedup

In addition to the gettimeofday(2) speedup listed in Section 2.5, “gettimeofday speedup”, the MRG Realtime kernel contains a further gettimeofday performance optimization. This method caches the most recently used time value in a global system file. If another gettimeofday call is performed within the ms (hz) then it is not necessary re-read the hardware clock. As a result, applications which do not require microsecond precision benefit.

Enable the MRG Realtime `gettimeofday` speedup

This setting is not enabled by default. When you start it, it needs to be enabled on a global basis.

Firstly you will need to append the line “kernel.vsyscall64 = 2” to the /etc/sysctl.conf file. This causes the gettimeofday function to be performed entirely in user-space, removing the system call overhead.
```
echo "kernel.vsyscall64 = 2" >> /etc/sysctl.conf
```
To make the change effective immediately and persistent between reboots, use the -w option with the sysctl command to update the setting:
```
/sbin/sysctl -w kernel.vsyscall64=2
```

Related Manual Pages

For more information, or for further reading, the following man pages are related to the information given in this section.

sysctl(8)
gettimeofday(2)