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    SubjectRe: TIF_NOHZ can escape nonhz mask? (Was: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases)
    On 07/31, Frederic Weisbecker wrote:
    >
    > 2014-07-31 20:47 GMT+02:00 Frederic Weisbecker <fweisbec@gmail.com>:
    > > On Thu, Jul 31, 2014 at 08:12:30PM +0200, Oleg Nesterov wrote:
    > >> On 07/31, Frederic Weisbecker wrote:
    > > No, because preempt_schedule_irq() does the ctx_state save and restore with
    > > exception_enter/exception_exit.
    >
    > Similar thing happens with schedule_user().
    >
    > preempt_schedule_irq() handles kernel preemption and schedule_user()
    > the user preemption. On both cases we save and restore the context
    > tracking state.
    >
    > This might be the missing piece you were missing :)

    YYYYYEEEEESSSS, thanks!!

    And in fact I was going to suggest to add this logic into preempt schedule
    paths to improve the situation if we can't make TIF_NOHZ per-cpu.

    But Frederic, perhaps I'll return here tomorrow with another question, it
    is too late for me now ;)

    Thanks!

    Oleg.



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