On Mon, Jun 19, 2006 at 05:20:31PM -0400, Theo Schlossnagle wrote:
> Heh. Syscall probes and FBT probes in Dtrace have zero overhead.
> User-space probes do have overhead, but it is only a few instructions
> (two I think). Besically, the probe points are replaced by illegal
> instructions and the kernel infrastructure for Dtrace will fasttrap
> the ops and then act. So, it is tiny tiny overhead. Little enough
> that it isn't unreasonable to instrument things like s_lock which are
> tiny.
If someone wanted to, they should be able to do benchmarking with the
DTrace patches on pgFoundry to see the overhead of just having the
probes in, and then having the probes in and actually using them. If you
*really* want to see the difference, add a probe in s_lock. :)
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461