On 07/20/2012 05:05 PM, Tejun Heo wrote:

Hey, Peter.

On Fri, Jul 20, 2012 at 05:45:40PM +0200, Peter Zijlstra wrote:

quoted

quoted

So, Peter, why does cpuset mangle with cgroup_mutex?  What guarantees
does it need?  Why can't it work on "changed" notification while
caching the current css like blkcg does?

I've no clue sorry.. /me goes stare at this stuff.. Looks like something
Paul Menage did when he created cgroups. I'll have to have a hard look
at all that to untangle this. Not something obvious to me.

Yeah, it would be great if this can be untangled.  I really don't see
any other reasonable way out of this circular locking mess.  If cpuset
needs stable css association across certain period, the RTTD is
caching the css by holding its ref and synchronize modifications to
that cache, rather than synchronizing cgroup operations themselves.

Thanks.

IIRC, cpuset can insert a task into an existing cgroup itself. Besides
that, it needs go have a stable vision of the cpumask used by all tasks
in the cgroup.

But this is what I remember from the top of my head, and I am still
officially on vacations....

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