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    SubjectRe: [Patch 4/7] Add sysctl for delay accounting
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    On Mon, 2006-02-27 at 14:34 +0530, Dipankar Sarma wrote:
    > On Mon, Feb 27, 2006 at 09:42:23AM +0100, Arjan van de Ven wrote:
    > > On Mon, 2006-02-27 at 03:38 -0500, Shailabh Nagar wrote:
    > > > Arjan van de Ven wrote:
    > > >
    > > > The function needs to allocate task_delay_info structs for all tasks
    > > > that might
    > > > have been forked since the last time delay accounting was turned off.
    > > > Either we have to count how many such tasks there are, or preallocate
    > > > nr_tasks (as an upper bound) and then use as many as needed.
    > >
    > > it generally feels really fragile, especially with the task enumeration
    > > going to RCU soon. (eg you'd lose the ability to lock out new task
    > > creation)
    >
    > I haven't yet seen any RCU-based code that does this. Can you point out
    > what patches you are talking about ? As of 2.6.16-rc4 and -rt15,
    > AFAICS, you can count tasks by holding the read side of tasklist_lock.
    > Granted it is a bit ugly to repeat this in order to overcome
    > the race on dropping tasklist_lock for allocation.

    there are several people (Christoph for one) who are working on making
    the tasklist_lock go away entirely in favor of RCU-like locking...

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