From owner-freebsd-current  Tue Jan 15 22: 3:45 2002
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From: Bruce Evans <bde@zeta.org.au>
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To: David Wolfskill <david@catwhisker.org>
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Subject: RE: -CURRENT as of 14 Jan seems slow
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On Tue, 15 Jan 2002, David Wolfskill wrote:

> >Date: Tue, 15 Jan 2002 16:46:17 -0800 (PST)
> >From: John Baldwin <jhb@FreeBSD.org>
> >Two questions:
>
> >1) Do you have WITNESS on in your kernel config?
>
> Yes, in both the build machine & the laptop -- since before I made a
> "local" hierarchy within my CVS repository (September 9, 2001).
>
> >2) If yes, have you tried building with a kernel without witness?
>
> No, not since I put it in to re-sync with GENERIC.  I could try that, I
> suppose -- but as noted, I've had WITNESS in there for a while; something
> seems to have changed during that one 24-hr. period that affected things
> rather radically.  And I thought it notable.  :-}
>
> I gather no one else has noticed this?

File locking seems to cause only the usual few percent of slowdown for
each round of major locking changes.  I haven't completed benchmarking
the file locking pessimizations.  I don't use WITNESS or INVARIANTS
for benchmarking of course.  Maybe the file locking changes cause much
larger pessimizations when WITNESS is turned on than most locking
changes.  I can see how they might: WITNESS seemed to slow down creation
and destruction of mutexes more than most mutex operations last time I
checked, and there is a descriptor for each file and each file descriptor.

Bruce


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