[dtrace-discuss] dtrace wired issue

Bryan Cantrill
Mon, 14 Jan 2008 14:46:49 -0000

On Mon, Jan 14, 2008 at 09:16:34PM +0800, Aubrey Li
wrote:
> On Jan 14, 2008 8:52 PM, Sean McGrath - Sun Microsystems Ireland
> <sean.mcgrath at sun.com> wrote:
> > Aubrey Li stated:
> > < Every first time to run dtrace command after the system boot up,
> > < It takes a very long time to get response.
> > < But the second time is OK, as follows:
> > <
> > < # time dtrace -l > /dev/null
> > <
> > < real    4m8.011s
> > < user    0m0.116s
> > < sys     0m2.420s
> >
> >   This first time is probably when the kernel is loading the dtrace
modules.
> >   Though still seems slow, 4 minutes.
> >     What kind of system (cpu speed etc) is the machine ?
>
> # psrinfo -vp
> The physical processor has 2 virtual processors (0 1)
>   x86 (GenuineIntel 10674 family 6 model 23 step 4 clock 2400 MHz)
>         Intel(r) CPU                  @ 2.40GHz
>
> So, I failed to understand the modules loading needs 4 minutes.

Yes, this is definitely fishy.  Is this a highly memory constrained system?
If you "modunload -i 0" enough times to get dtrace(7D) unloaded (that
is, "dtrace" doesn''t appear in modinfo), does it again take 4
minutes?
As you can imagine, it''s a little tough to investigate this problem
because
we can''t use DTrace to do it! ;)

> > < # time dtrace -l > /dev/null
> > <
> > < real    0m0.632s
> > < user    0m0.075s
> > < sys     0m0.553s

And 600+ milliseconds is still a long time.  How many probes are we talking
about here?

	- Bryan

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Bryan Cantrill, Sun Microsystems FishWorks.       http://blogs.sun.com/bmc