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    SubjectRe: [patch,v2] bdi: add a user-tunable cpu_list for the bdi flusher threads
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    Jens Axboe <jaxboe@fusionio.com> writes:

    > On 2012-12-03 19:53, Jeff Moyer wrote:
    >> Hi,
    >>
    >> In realtime environments, it may be desirable to keep the per-bdi
    >> flusher threads from running on certain cpus. This patch adds a
    >> cpu_list file to /sys/class/bdi/* to enable this. The default is to tie
    >> the flusher threads to the same numa node as the backing device (though
    >> I could be convinced to make it a mask of all cpus to avoid a change in
    >> behaviour).
    >
    > Looks sane, and I think defaulting to the home node is a sane default.
    > One comment:
    >
    >> + ret = cpulist_parse(buf, newmask);
    >> + if (!ret) {
    >> + spin_lock(&bdi->wb_lock);
    >> + task = wb->task;
    >> + if (task)
    >> + get_task_struct(task);
    >> + spin_unlock(&bdi->wb_lock);
    >
    > bdi->wb_lock needs to be bh safe. The above should have caused lockdep
    > warnings for you.

    No lockdep complaints. I'll double check that's enabled (but I usually
    have it enabled...).

    >> @@ -437,6 +488,14 @@ static int bdi_forker_thread(void *ptr)
    >> spin_lock_bh(&bdi->wb_lock);
    >> bdi->wb.task = task;
    >> spin_unlock_bh(&bdi->wb_lock);
    >> + mutex_lock(&bdi->flusher_cpumask_mutex);
    >> + ret = set_cpus_allowed_ptr(task,
    >> + bdi->flusher_cpumask);
    >> + mutex_unlock(&bdi->flusher_cpumask_mutex);
    >
    > It'd be very useful if we had a kthread_create_cpu_on_cpumask() instead
    > of a _node() variant, since the latter could easily be implemented on
    > top of the former. But not really a show stopper for the patch...

    Hmm, if it isn't too scary, I might give this a try.

    Thanks!
    Jeff


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