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    SubjectRe: [PATCH repost] sched: export sched_set/getaffinity to modules
    On Thu, Jul 01, 2010 at 02:32:43PM +0200, Peter Zijlstra wrote:
    > On Thu, 2010-07-01 at 14:55 +0300, Michael S. Tsirkin wrote:
    >
    > > > - why can't it set the kernel thread's affinity too?
    > >
    > > It can. However: the threads are started internally by the driver
    > > when qemu does an ioctl. What we want to do is give it a sensible
    > > default affinity. management tool can later tweak it if it wants to.
    >
    > So have that ioctl return the tid of that new fancy thread and then set
    > its affinity, stuff it in cgroup, whatever you fancy.
    >
    > > > - what happens if someone changes the tasks' affinity?
    > >
    > > We would normally create a cgroup including all internal
    > > tasks, making it easy to find and change affinity for
    > > them all if necessary.
    >
    > And to stuff them in a cgroup you also need the tid, at which point it
    > might as well set the affinity from userspace, right?

    We also put it in a cgroup transparently. I think that it's actually
    important to do it on thread creation: if we don't, malicious userspace
    can create large amount of work exceeding the cgroup limits.

    And the same applies so the affinity, right? If the qemu process
    is limited to a set of CPUs, isn't it important to make
    the kernel thread that does work our behalf limited to the same
    set of CPUs?

    --
    MST


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