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    SubjectRe: [PATCH 2.6.16-mm1 2/2] sched_domains: Allocate sched_groups dynamically
    I have reviewed Srivatsa's code back then and made sure it fixes
    the problem in the presence of multi-core too. Based on my review,
    I provided feedback to Srivatsa then.

    In short, multi-core was broken too and Srivatsa's patch fixed it.


    On Thu, Jul 06, 2006 at 05:01:51PM -0700, Paul Jackson wrote:
    > Several months ago, Srivatsa wrote:
    > > I couldn't test this on a multi-core machine, since I don't think we
    > > have one in our lab.
    > >
    > > Suresh, would you mind testing the patch on a multi-core machine, in case you
    > > have access to one?
    > >
    > > Basically you would need to do create a exclusive CPUset with one CPU in it
    > > (ensure that its sibling in the same core is not part of the same
    > > CPUset). As soon as you make the CPUset exclusive, you would hit some
    > > kind of hang. With this patch, the hang should go away.
    > Summary: Where do we stand with multi-core and this bug?
    > I don't see a reply from Suresh on whether he could test on multi-core.
    > I finally happened to be running on a hyper-threaded box last week,
    > and stumbled over this bug that Srivatsa's patch fixes. Hawkes
    > remembered Srivatsa's patch, I tried it, and it worked. Thanks!
    > But now I'm quite confused as to the situation with multi-core.
    > Details of my confusions, for the bored:
    > From Srivatsa's remark, I would have guessed that multi-core was
    > at risk for this bug too, but Srivatsa was hopeful that his patch
    > would fix that too.
    > Early this week, a couple of people who shall remain anonymous here
    > raised the question of whether we had the same problem with multi-core.
    > One of them believed that multi-core did have the same problem.
    > I got a little time on a multi-core system this morning to test it,
    > and while running what I -thought- was a kernel -without- Srivatsa's
    > patch, I could not find any problem. I made a cpuset with just a
    > single logical cpu in it, and marked it cpu_exclusive, and the
    > system did not hang.
    > It will be another day before I can get on that multi-core system
    > again to verify my findings.
    > I was hoping that someone could actually -read- this code and state
    > with confidence that one of the following held:
    > * it was already working ok on multi-core (a one CPU cpu_exclusive cpuset),
    > * it was broken, but Srivatsa's patch fixes it, or
    > * it's still broken, even with Srivatsa's patch.
    > I tried a couple of times to read the code myself, but could not
    > make any headway there.
    > So ... what's up with multi-core and this bug?
    > --
    > I won't rest till it's the best ...
    > Programmer, Linux Scalability
    > Paul Jackson <> 1.925.600.0401
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