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Re: [RFC PATCH v2] membarrier: expedited private command

From "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Newsgroups linux.kernel
Subject Re: [RFC PATCH v2] membarrier: expedited private command
Date 2017-08-02 01:40 +0200
Message-ID <u9OVz-24F-5@gated-at.bofh.it> (permalink)
References (5 earlier) <u9Azf-Lh-13@gated-at.bofh.it> <u9C82-20u-17@gated-at.bofh.it> <u9CB3-2At-17@gated-at.bofh.it> <u9Fpf-4wG-21@gated-at.bofh.it> <u9GbE-52o-19@gated-at.bofh.it>
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On Tue, Aug 01, 2017 at 04:16:54PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 01, 2017 at 06:23:09AM -0700, Paul E. McKenney wrote:
> > On Tue, Aug 01, 2017 at 12:22:03PM +0200, Peter Zijlstra wrote:
> > 
> > [ . . . ]
> > 
> > > As to scheduler IPIs, those are limited to the CPUs the user is limited
> > > to and are rate limited by the wakeup-latency of the tasks. After all,
> > > all the time a task is runnable but not running, wakeups are no-ops.
> > 
> > Can't that wakeup-latency limitation be overcome by a normal user simply
> > by having lots of tasks to wake up, which then go back to sleep almost
> > immediately?  Coupled with very a low-priority CPU-bound task on each CPU?
> 
> Let me put it like this; there is no way to cause more interference
> using IPIs then there is simply running while(1) loops ;-)

Very good, that does give us some guidance, give or take context switches
happening during the IPI latency window.  ;-)

							Thanx, Paul

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Re: [RFC PATCH v2] membarrier: expedited private command Michael Ellerman <mpe@ellerman.id.au> - 2017-07-31 15:30 +0200
  Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-31 15:40 +0200
  Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-08-01 02:40 +0200
    Re: [RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-08-01 03:40 +0200
      Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-08-01 04:10 +0200
        Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-08-01 10:20 +0200
          Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-08-01 12:00 +0200
            Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-08-01 12:30 +0200
              Re: [RFC PATCH v2] membarrier: expedited private command Avi Kivity <avi@scylladb.com> - 2017-08-01 12:40 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-08-01 12:50 +0200
              Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-08-01 12:40 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-08-01 13:10 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-08-01 14:00 +0200
              Re: [RFC PATCH v2] membarrier: expedited private command "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-01 15:30 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-08-01 16:20 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-02 01:40 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-08-02 02:50 +0200

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