Re: [PATCHv7 00/33] kernel: Introduce Time Namespace

On Fri, 11 Oct 2019, Dmitry Safonov wrote:

We wrote two small benchmarks. The first one gettime_perf.c calls
clock_gettime() in a loop for 3 seconds. It shows us performance with
a hot CPU cache (more clock_gettime() cycles - the better):

        | before    | CONFIG_TIME_NS=n | host      | inside timens
--------------------------------------------------------------
        | 153242367 | 153567617        | 150933203 | 139310914
        | 153324800 | 153115132        | 150919828 | 139299761
        | 153125401 | 153686868        | 150930471 | 139273917
        | 153399355 | 153694866        | 151083410 | 139286081
        | 153489417 | 153739716        | 150997262 | 139146403
        | 153494270 | 153724332        | 150035651 | 138835612
-----------------------------------------------------------
avg     | 153345935 | 153588088        | 150816637 | 139192114
diff %  | 100       | 100.1            | 98.3      | 90.7

That host 98.3% number is weird and does not match the tests I did with the
fallback code I provided you. On my limited testing that fallback hidden in
the slowpath did not show any difference to the TIME_NS=n case when not
inside a time namespace.

Thanks,

	tglx