PERFORCE change 63396 for review

[John Baldwin]

On Thursday 21 October 2004 11:37 pm, Brian Fundakowski Feldman wrote:
> On Wed, Oct 20, 2004 at 12:58:26PM -0400, John Baldwin wrote:
> > On Tuesday 19 October 2004 06:19 pm, Julian Elischer wrote:
> > > John Baldwin wrote:
> > > >http://perforce.freebsd.org/chv.cgi?CH=63396
> > > >
> > > >Change 63396 by jhb at jhb_tibook on 2004/10/19 21:58:24
> > > >
> > > >	Update.
> > > >
> > > >Affected files ...
> > > >
> > > >.. //depot/projects/smpng/sys/notes#21 edit
> > > >
> > > >Differences ...
> > > >
> > > >==== //depot/projects/smpng/sys/notes#21 (text+ko) ====
> > > >
> > > >@@ -33,6 +33,10 @@
> > > >   - Untested
> > > > - Don't allow kthreads to get signalled and do bad things
> > > >   - Untested
> > > >+- Change amd64 to use [ls]fence instructions for memory barriers.
> > > >+  - Untested (and no hardware, maybe peter can test)
> > > >+- Turn off the ipiwakeups in 4BSD since the currently implementation
> > > > can +  lead to IPI deadlocks
> > >
> > > the implementation of IPIs or the implementation of IPIwakeup?
> >
> > Kind of hard to say.  The problem is if a CPU tries to send two IPI_AST's
> > without enabling interrupts in between.  The first IPI may not be
> > delivered when the second one is requested because the target of the
> > first IPI has interrupts disabled for some reason (doing a TLB shootdown
> > is the worst case scenario).  The other CPU won't enable interrupts to
> > allow the first AST until it's shootdown is acknowledged.  Since the
> > first IPI is never delivered, then the second IPI attempt will never be
> > able to deliver an IPI, resulting in either a panic or deadlock.  My quad
> > xeon is highly unstable on HEAD, btw, and this does seem to help it.
>
> Isn't this what I said a few weeks ago was probably the problem?

I have no idea, but ups@ brought this up a couple of weeks ago when we met for 
lunch.

-- 

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/