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    SubjectRe: [PATCH] stop on cpu lost
    On Thu, 22 Jun 2006 10:08:48 -0500 Nathan Lynch wrote:

    > Andrew Morton wrote:
    > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > > >
    > > > Now, when a task loses all of its allowed cpus because of cpu hot removal,
    > > > it will be foreced to migrate to not-allowed cpus.
    > > >
    > > > In this case, the task is not properly reconfigurated by a user before
    > > > cpu-hot-removal. Here, the task (and system) is in a unexpeced wrong state.
    > > > This migration is maybe one of realistic workarounds. But sometimes it will be
    > > > harmfull.
    > > > (stealing other cpu time, making bugs in thread controllers, do some unexpected
    > > > execution...)
    > > >
    > > > This patch adds sysctl "sigstop_on_cpu_lost". When sigstop_on_cpu_lost==1,
    > > > a task which losts is cpu will be stopped by SIGSTOP.
    > > > Depends on system management policy, mis-configurated applications are stopped.
    > > >
    > >
    > > Well that's a pretty unpleasant patch, isn't it?
    > >
    > > But I guess it's policy, and if we cannot think of anything better then we'll
    > > have to do it this way :(
    >
    > I tend to favor not changing the kernel to handle this case. We're
    > already making a best effort attempt to handle conflicting directives
    > from the admin. This is a policy that can be implemented in userspace
    > without much trouble.
    >
    > If we really want to keep the admin shooting himself in the foot,
    > wouldn't it be preferable to fail the offline operation if there are
    > user tasks exclusively bound to the cpu?

    Sounds much better than just killing the process.

    > While we're on the subject, what if there are interrupts bound to the
    > cpu you want to offline? Should we consider handling that case
    > differently as well?


    ---
    ~Randy
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