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    SubjectRe: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1]

    * Bill Huey <> wrote:

    > > > This patch moves put_task_struct() reaping into a thread instead
    > > > of an RCU callback function [...]
    > >
    > > had some time to think about it since yesterday: RCU reaping is done
    > > in softirqs (check out the softirq-rcu threads on your -rt box),
    > > that's why i removed the delayed-task-drop code to begin with. Now i
    > > dont doubt
    > It's correct from the standpoint of it being reaped in another thread,
    > so it fixed those crashes. But I pushed it down into another thread at
    > the request of Esben and his private discussion with Paul McKenney,
    > since a summary from Esben felt that call_rcu() was somehow less than
    > ideal to do that.

    but it _is_ already being reaped in another thread: softirq-rcu.
    Splitting that up any further will only fragment the context-switching
    and increases cache footprint - it wont (or rather, shouldnt) have any
    functional effect. (As a sidenote, i'm considering the unification of
    all 'same default priority' softirq threads into a single thread per
    CPU, to further reduce this cost of 'spreadout'.)

    > > that you saw crashes under 2.6.17 - but did you manage to figure out
    > > what the reason is for those crashes, and do those reasons really
    > > necessiate the pushing of task-reapdown into yet another set of
    > > kernel threads?
    > Unfortunately no. I even used Robert's .config on my machine. I added
    > a disk controller and networking device driver just to boot into his
    > configuration and I still couldn't replicated any of his kjournald
    > problems at all. If I had his hardware I'd have a better way of
    > replicating those problems and pound it out.

    ok, then i guess what we have left is to wait and see whether it still
    triggers with the current 2.6.18-rt codebase - maybe it triggers for
    someone in a scenario that is easier to debug.

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