On Friday, June 22, 2012 3:34:56 am Marius Strobl wrote: > On Fri, Jun 22, 2012 at 07:13:31AM +0000, Konstantin Belousov wrote: > > Author: kib > > Date: Fri Jun 22 07:13:30 2012 > > New Revision: 237434 > > URL: http://svn.freebsd.org/changeset/base/237434 > > > > Log: > > Use struct vdso_timehands data to implement fast gettimeofday(2) and > > clock_gettime(2) functions if supported. The speedup seen in > > microbenchmarks is in range 4x-7x depending on the hardware. > > > > Only amd64 and i386 architectures are supported. Libc uses rdtsc and > > kernel data to calculate current time, if enabled by kernel. > > I don't know much about x86 CPUs but is my understanding correct > that TSCs are not synchronized in any way across CPUs, i.e. > reading it on different CPUs may result in time going backwards > etc., which is okay for this application though?
Hmm, in practice I have found that on modern x86 CPUs (Penryn and later) the TSC is in fact sychronized across packages at work. At least, when I measure skew across packages it appears to be consistent with the time it would take a write to propagate from one to the other. -- John Baldwin _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
