Performance of 4.x vs 5.x (Re: Lifetime of FreeBSD branches)

Jon Dama jd at
Wed May 25 15:33:53 PDT 2005

Could this be quantified by setting up a synthetic experiement:

1) one machine uses dummynet to generate a uniform packet/sec stream
2) another machine has a process receiving those packets and recording
   their arrival relative to the local TSC.  afaik, the TSC is the only
   source of wall-time that doesn't involve a system call.  Is that right?
   Are the TSCs synchronized on SMP systems?
3) Generate another source of activity on the receiving machine to
   estimate the effect of PREEMPTION relative to the (lack of) quiescence.
4) use the jitter in the TSC deltas to infer the effect of preemption


On Thu, 26 May 2005, Bjarne Wichmann Petersen wrote:

> On Wednesday 25 May 2005 23:45, Kris Kennaway wrote:
> > On Wed, May 25, 2005 at 11:42:01PM +0200, Bjarne Wichmann Petersen wrote:
> > > I've had PREEMTION enabled in 5-STABLE for at couple of month and had the
> > > opposite experience. Eg. when clicking on a file in a fileselector (I'm
> > > using KDE) it would take 2-3 seconds before the file got highlighted.
> > > After disabling PREEMTION again responsetime seems to have improved.
> > Are you running 5.4-RELEASE or later?
> Later (5.4-STABLE).
> Hmm... did a little testing. Sometimes I *still* get "long" responsetimes with
> PREEMPTION disabled in a seemingly random order.
> Bjarne
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