From: Peter Zijlstra <peterz@infradead.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Michael Ellerman <mpe@ellerman.id.au>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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 10:12:30 +0200 [thread overview]
Message-ID: <20170801081230.GF6524@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20170801120047.61c59064@roar.ozlabs.ibm.com>
On Tue, Aug 01, 2017 at 12:00:47PM +1000, Nicholas Piggin wrote:
> Thanks for this, I'll take a look. This should be a good start as a stress
> test, but I'd also be interested in some application. The reason being that
> for example using runqueue locks may give reasonable maximum throughput
> numbers, but could cause some latency or slowdown when it's used in more
> realistic scenario.
Given this is an unprivileged interface we have to consider DoS and
other such lovely things. And since we cannot use mm_cpumask() we're
stuck with for_each_online_cpu().
Combined that means that using rq->lock is completely out of the
question, some numbnut doing 'for (;;) sys_membarrier();' can
completely wreck the system.
Yes, it might work for 'normal' workloads, but the interference
potential is just too big.
I have the same problem with Paul's synchronize_rcu_expedited() patch,
that is a machine wide IPI spray and will interfere with unrelated work.
next prev parent reply other threads:[~2017-08-01 8:13 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 [this message]
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
2017-08-02 0:45 ` Nicholas Piggin
2017-07-28 15:36 ` Mathieu Desnoyers
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