I was wondering if anyone here has NTP servers that are handling so
much NTP traffic that the CPU is the limiting factor and if there is
any interest in optimizing chrony for better performance.

The Linux kernel has special system calls that can receive or send
multiple packets at once. This reduces the amount of time spent in
switching between the kernel and user-space. I ran some experiments
and it seems they do improve the maximum packet rate nicely. On a
PC-based server the rate improved from about 210000/sec to 260000/sec
when the receiving code was modified, and to about 350000/sec when
also the sending code was modified. On a low-end router running OpenWrt
the rate went from about 2200/sec to 2800/sec when the receiving was

This was just a quick hack to see how it works. If it should be
implemented properly, improving the receiving code would be easy, but
the sending would be much more difficult and it may also have a
negative effect on the accuracy. Would there be any interest in
improvements like that? I'm considering to do the former, but not the

Miroslav Lichvar

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