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Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option
Date 2017-07-25 21:00 +0200
Message-ID <u7ddM-6sM-5@gated-at.bofh.it> (permalink)
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On Tue, Jul 25, 2017 at 10:17:01AM -0700, Paul E. McKenney wrote:

> > munmap() TLB invalidate is limited to those CPUs that actually ran
> > threads of their process, while this is machine wide.
> 
> Or those CPUs running threads of any process mapping the underlying file
> or whatever.

That doesn't sound right. munmap() of a shared file only invalidates
this process's map of it.

Swapping a file page otoh will indeed touch the union of cpumasks over
all processes mapping that page.

> And in either case, this can span the whole machine.  Plus
> there are a number of other ways for users to do on-demand full-system
> IPIs, including any number of ways to wake up large numbers of CPUs,
> including from unrelated processes.

Which are those? I thought we significantly reduced those with the nohz
full work. Most IPI uses now first check if a CPU actually needs the IPI
before sending it IIRC.

> But I do plan to add another alternative that is limited to threads of
> the running process.  I will be carrying both versions to enable those
> who have been bugging me about this to do testing.

Sending IPIs to mm_cpumask() might be better than expedited, but I'm
still hesitant. Just because people want it doesn't mean its a good
idea. We need to weight this against the potential for abuse.

People want userspace preempt disable, no matter how hard they want it,
they're not getting it because its a completely crap idea.

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Thread

[PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 00:00 +0200
  Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Boqun Feng <boqun.feng@gmail.com> - 2017-07-25 06:30 +0200
    Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 18:30 +0200
  Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-25 15:20 +0200
    Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 18:50 +0200
  Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-25 18:40 +0200
    Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 18:50 +0200
      Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-25 19:10 +0200
        Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 19:20 +0200
          Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-25 21:00 +0200
            Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 21:40 +0200
              Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-25 22:30 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-25 23:20 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-26 00:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-26 00:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-26 00:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 02:10 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-26 09:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 17:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-26 20:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 20:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-26 22:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 23:20 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 03:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-27 14:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 16:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 12:30 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 17:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 11:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 12:20 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Will Deacon <will.deacon@arm.com> - 2017-07-27 12:30 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 15:20 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 02:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-26 09:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 17:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 10:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 15:10 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 15:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 16:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 16:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 16:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 16:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 17:30 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Boqun Feng <boqun.feng@gmail.com> - 2017-07-27 16:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 16:20 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Boqun Feng <boqun.feng@gmail.com> - 2017-07-27 16:30 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 16:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Will Deacon <will.deacon@arm.com> - 2017-07-27 16:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Boqun Feng <boqun.feng@gmail.com> - 2017-07-27 16:50 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 17:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Will Deacon <will.deacon@arm.com> - 2017-07-26 11:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-26 17:50 +0200
              Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 12:20 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 15:00 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option Peter Zijlstra <peterz@infradead.org> - 2017-07-27 15:40 +0200
                Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-27 16:40 +0200

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