Re: [PATCH 2.6.16-mm1 2/2] sched_domains: Allocate sched_groups dynamically

[Siddha, Suresh B]

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.

thanks,
suresh

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 <pj@xxxxxxx> 1.925.600.0401
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