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Message-ID: <1405996274.5177.25.camel@marge.simpson.net> Date: Tue, 22 Jul 2014 04:31:14 +0200 From: Mike Galbraith <umgwanakikbuti@...il.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Darren Hart <dvhart@...ux.intel.com>, Andy Lutomirski <luto@...capital.net>, Peter Zijlstra <peterz@...radead.org>, Andi Kleen <andi@...stfloor.org>, Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...nel.org>, Davidlohr Bueso <davidlohr@...com>, Heiko Carstens <heiko.carstens@...ibm.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, Jason Low <jason.low2@...com>, Scott J Norton <scott.norton@...com>, Robert Haas <robertmhaas@...il.com> Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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