From: Peter Zijlstra <peterz@infradead.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
lkml <linux-kernel@vger.kernel.org>, Tejun Heo <tj@kernel.org>,
Dmitry Shmidt <dimitrysh@google.com>,
Rom Lemarchand <romlem@google.com>,
Colin Cross <ccross@google.com>, Todd Kjos <tkjos@google.com>
Subject: Re: [PATCH v2] locking/percpu-rwsem: Optimize readers and reduce global impact
Date: Wed, 10 Aug 2016 09:56:06 +0200 [thread overview]
Message-ID: <20160810075606.GK6879@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CALAqxLXLf_hB0xQ_vnBYoHyDF2-Bkh9GznLQK=ikYFdcw5u3WQ@mail.gmail.com>
On Tue, Aug 09, 2016 at 04:47:38PM -0700, John Stultz wrote:
> On Tue, Aug 9, 2016 at 2:51 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > Currently the percpu-rwsem switches to (global) atomic ops while a
> > writer is waiting; which could be quite a while and slows down
> > releasing the readers.
> >
> > This patch cures this problem by ordering the reader-state vs
> > reader-count (see the comments in __percpu_down_read() and
> > percpu_down_write()). This changes a global atomic op into a full
> > memory barrier, which doesn't have the global cacheline contention.
> >
> > This also enables using the percpu-rwsem with rcu_sync disabled in order
> > to bias the implementation differently, reducing the writer latency by
> > adding some cost to readers.
>
> So this by itself doesn't help us much, but including the following
> from Oleg does help quite a bit:
Correct, Oleg was going to send his rcu_sync rework on top of this. But
since its holiday season things might be tad delayed.
next prev parent reply other threads:[~2016-08-10 19:12 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-09 9:51 [PATCH v2] locking/percpu-rwsem: Optimize readers and reduce global impact Peter Zijlstra
2016-08-09 23:47 ` John Stultz
2016-08-10 7:56 ` Peter Zijlstra [this message]
2016-08-10 17:09 ` Oleg Nesterov
[not found] ` <CAH7ZN-zXrenrbbcmvZ+biNozYe21jw6fULopG=g9-xRwWHE6nw@mail.gmail.com>
[not found] ` <5a2cc178ee03466fa3b104f8f28b44ff@NASANEXM02C.na.qualcomm.com>
2016-08-13 1:44 ` Om Dhyade
2016-08-24 21:16 ` John Stultz
2016-08-24 21:30 ` Tejun Heo
2016-08-24 22:50 ` John Stultz
2016-08-26 2:14 ` John Stultz
2016-08-26 12:51 ` Tejun Heo
2016-08-26 16:47 ` Dmitry Shmidt
2016-08-26 20:10 ` Om Dhyade
2016-08-11 16:54 ` [PATCH] cgroup: avoid synchronize_sched() in __cgroup_procs_write() Oleg Nesterov
2016-08-18 10:59 ` [tip:locking/core] locking, rcu, cgroup: Avoid " tip-bot for Peter Zijlstra
2016-08-18 13:41 ` tip-bot for Peter Zijlstra
2016-08-31 5:21 ` [v2] locking/percpu-rwsem: Optimize readers and reduce global impact Guenter Roeck
2016-08-31 8:09 ` Peter Zijlstra
2016-08-31 13:41 ` Guenter Roeck
2016-08-31 13:47 ` Guenter Roeck
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