Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once

Paul Menage
2009-08-04T18:49:06Z

On Mon, Aug 3, 2009 at 12:45 PM, Serge E. Hallyn<serue@us.ibm.com> wrote:
>
> This is probably a stupid idea, but...  what about having zero
> overhead at clone(), and instead, at cgroup_task_migrate(),
> dequeue_task()ing all of the affected threads for the duration of
> the migrate?
>

Or a simpler alternative - rather than taking the thread group
leader's rwsem in cgroup_fork(), always take current's rwsem. Then
you're always locking a (probably?) local rwsem and minimizing the
overhead. So not quite zero overhead in the fork path, but I'd be
surprised if it was measurable. In cgroup_attach_proc() you then have
to take the rwsem of every thread in the process. Kind of the
equivalent of a per-threadgroup big-reader lock.

Paul