From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Darren Hart <dvhart@linux.intel.com>,
Andy Lutomirski <luto@amacapital.net>,
Peter Zijlstra <peterz@infradead.org>,
Andi Kleen <andi@firstfloor.org>,
Waiman Long <Waiman.Long@hp.com>, Ingo Molnar <mingo@kernel.org>,
Davidlohr Bueso <davidlohr@hp.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
Jason Low <jason.low2@hp.com>,
Scott J Norton <scott.norton@hp.com>,
Robert Haas <robertmhaas@gmail.com>
Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex
Date: Tue, 22 Jul 2014 04:31:14 +0200 [thread overview]
Message-ID: <1405996274.5177.25.camel@marge.simpson.net> (raw)
In-Reply-To: <20140721213457.46623e2f@gandalf.local.home>
On Mon, 2014-07-21 at 21:34 -0400, Steven Rostedt wrote:
> I was telling Robert that if futexes get optimistic spinning, he should
> reconsider their use of userspace spinlocks in favor of this, because
> I'm pretty sure that they will see a great improvement.
My (dated) experience with pgsql says you're likely right.
Once upon a time, preempting a userspace spinlock owner caused pgsql to
collapse into a quivering heap. The scheduler trying to hand the CPU
back to a preempted task instead of selecting what was strictly speaking
the most deserving task afterward (LAST_BUDDY) let pgsql+oltp scale nice
and flat instead of self destructing, but the root cause of collapse was
spinners lacking knowledge. With spin done in kernel, you can know
when spinning is a waste of perfectly good cycles.
-Mike
next prev parent reply other threads:[~2014-07-22 2:31 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-21 15:24 Waiman Long
2014-07-21 15:24 ` [RFC PATCH 1/5] futex: add new exclusive lock & unlock command codes Waiman Long
2014-07-21 16:42 ` Thomas Gleixner
2014-07-22 18:22 ` Waiman Long
2014-07-22 21:00 ` Thomas Gleixner
2014-07-21 15:24 ` [RFC PATCH 2/5] futex: add optimistic spinning to FUTEX_SPIN_LOCK Waiman Long
2014-07-21 17:15 ` Davidlohr Bueso
2014-07-22 18:46 ` Waiman Long
2014-07-21 20:17 ` Jason Low
2014-07-22 19:34 ` Waiman Long
2014-07-21 15:24 ` [RFC PATCH 3/5] spinning futex: move a wakened task to spinning Waiman Long
2014-07-21 15:24 ` [RFC PATCH 4/5] spinning futex: put waiting tasks in a sorted rbtree Waiman Long
2014-07-21 15:24 ` [RFC PATCH 5/5] futex, doc: add a document on how to use the spinning futexes Waiman Long
2014-07-21 15:45 ` Randy Dunlap
2014-07-22 3:19 ` Waiman Long
2014-07-21 16:42 ` [RFC PATCH 0/5] futex: introduce an optimistic spinning futex Andi Kleen
2014-07-21 16:45 ` Andi Kleen
2014-07-21 17:20 ` Darren Hart
[not found] ` <CFF29A00.9D44A%dvhart@linux.intel.com>
2014-07-21 17:41 ` Darren Hart
2014-07-21 20:16 ` Thomas Gleixner
2014-07-21 21:27 ` Peter Zijlstra
2014-07-21 21:31 ` Andy Lutomirski
2014-07-21 21:47 ` Thomas Gleixner
2014-07-21 22:41 ` Darren Hart
2014-07-22 1:01 ` Thomas Gleixner
2014-07-22 1:34 ` Steven Rostedt
2014-07-22 2:31 ` Mike Galbraith [this message]
2014-07-22 3:06 ` Davidlohr Bueso
2014-07-22 7:47 ` Peter Zijlstra
2014-07-22 8:39 ` Thomas Gleixner
2014-07-22 8:48 ` Peter Zijlstra
2014-07-22 9:59 ` Thomas Gleixner
2014-07-22 20:25 ` Waiman Long
2014-07-22 20:52 ` Thomas Gleixner
2014-07-22 20:21 ` Waiman Long
2014-07-22 21:03 ` Thomas Gleixner
2014-07-22 0:32 ` Davidlohr Bueso
2014-07-22 7:35 ` Peter Zijlstra
2014-07-21 21:43 ` Thomas Gleixner
2014-07-21 18:24 ` Thomas Gleixner
2014-07-22 18:35 ` Waiman Long
2014-07-22 18:28 ` Waiman Long
2014-07-23 4:55 ` Mike Galbraith
2014-07-23 6:57 ` Peter Zijlstra
2014-07-23 7:25 ` Mike Galbraith
2014-07-23 7:35 ` Peter Zijlstra
2014-07-23 7:39 ` Mike Galbraith
2014-07-23 7:52 ` Peter Zijlstra
2014-07-21 21:18 ` Ingo Molnar
2014-07-21 21:41 ` Thomas Gleixner
2014-07-22 19:36 ` Waiman Long
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