Fwd: [tor-dev] gettimeofday() Syscall Issues

grarpamp grarpamp at gmail.com
Fri Jan 2 23:15:07 UTC 2015

On Fri, Jan 2, 2015 at 12:24 PM, Konstantin Belousov
<kostikbel at gmail.com> wrote:
> On Fri, Jan 02, 2015 at 09:09:34AM -0500, grarpamp wrote:
>> Some recent FreeBSD related questions in this app area.
> What is the question ?
> As a background, I can repeat that FreeBSD implements syscall-less
> gettimeofday() and clock_gettime() for x86 machines which have
> usable RDTSC.  The selection of the timecounter can be verified
> by sysctl kern.timecounter.hardware, and enabled by default fast
> gettimeofday(2) can be checked by sysctl kern.timecounter.fast_gettime.
> On some Nehalem machine, I see it doing ~30M calls/sec with enabled
> fast_gettime, and ~6.25M calls/sec with disabled fast_gettime. This is
> measured on 2.8GHz Core i7 930 with src/tools/tools/syscall_timing.
> Check your timecounter hardware.  Since it was noted that the tests
> were done in VM, check the quality of RDTSC emulation in your hypervisor.


Maybe I can just refer non subscribers out to the two lists above that way
in case anyone sees anything interesting they can join/comment as desired.

Background might be that Tor operators have some large relays on *BSD
and were looking to validate, and ways to improve, performance there.



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