From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-kernel <linux-kernel@vger.kernel.org>,
Boqun Feng <boqun.feng@gmail.com>, Andrew Hunter <ahh@google.com>,
maged michael <maged.michael@gmail.com>,
gromer <gromer@google.com>, Avi Kivity <avi@scylladb.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Dave Watson <davejwatson@fb.com>
Subject: Re: [RFC PATCH v2] membarrier: expedited private command
Date: Tue, 1 Aug 2017 16:32:03 -0700 [thread overview]
Message-ID: <20170801233203.GO3730@linux.vnet.ibm.com> (raw)
In-Reply-To: <20170801141654.qredbzshlz47lfxy@hirez.programming.kicks-ass.net>
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
next prev parent reply other threads:[~2017-08-01 23:32 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-27 21:13 [RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers
2017-07-27 22:13 ` Paul E. McKenney
2017-07-27 22:41 ` Mathieu Desnoyers
2017-07-27 22:57 ` Paul E. McKenney
2017-07-28 8:55 ` Peter Zijlstra
2017-07-28 11:10 ` Peter Zijlstra
2017-07-28 11:57 ` Peter Zijlstra
2017-07-28 15:38 ` Mathieu Desnoyers
2017-07-28 16:46 ` Peter Zijlstra
2017-07-28 17:06 ` Mathieu Desnoyers
2017-07-29 1:58 ` Nicholas Piggin
2017-07-29 9:23 ` Peter Zijlstra
2017-07-29 9:45 ` Nicholas Piggin
2017-07-29 9:48 ` Nicholas Piggin
2017-07-29 10:51 ` Peter Zijlstra
2017-07-31 19:31 ` Mathieu Desnoyers
2017-07-31 13:20 ` Michael Ellerman
2017-07-31 13:36 ` Peter Zijlstra
2017-08-01 0:35 ` Nicholas Piggin
2017-08-01 1:33 ` Mathieu Desnoyers
2017-08-01 2:00 ` Nicholas Piggin
2017-08-01 8:12 ` Peter Zijlstra
2017-08-01 9:57 ` Nicholas Piggin
2017-08-01 10:22 ` Peter Zijlstra
2017-08-01 10:32 ` Avi Kivity
2017-08-01 10:46 ` Peter Zijlstra
2017-08-01 10:39 ` Nicholas Piggin
2017-08-01 11:00 ` Peter Zijlstra
2017-08-01 11:54 ` Nicholas Piggin
2017-08-01 13:23 ` Paul E. McKenney
2017-08-01 14:16 ` Peter Zijlstra
2017-08-01 23:32 ` Paul E. McKenney [this message]
2017-08-02 0:45 ` Nicholas Piggin
2017-07-28 15:36 ` Mathieu Desnoyers
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