Re: [PATCH 3/5] lockstat: core infrastructure

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2007-05-29 at 13:28 -0700, Daniel Walker wrote:
> On Tue, 2007-05-29 at 14:52 +0200, Peter Zijlstra wrote:
> > +       now = sched_clock();
> > +       waittime = now - hlock->waittime_stamp;
> > + 
> 
> It looks like your using sched_clock() through out .. It's a little
> troubling considering the constraints on the function .. Most
> architecture implement a jiffies sched_clock() w/ 1 millisecond or worse
> resolution.. I'd imagine a millisecond hold time is pretty rare, even a
> millisecond wait time might be fairly rare too ..  There's also no
> guarantee that sched_clock timestamps off two different cpu's can be
> compared (or at least that's my understanding) ..

All valid points, however.. calling anything more expensive 2-3 times
per lock acquisition is going to be _very_ painful.

Also, IMHO the contention count vs the acquisition count is the most
interesting number, the times are just a nice bonus (if and when they
work).