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Message-ID: <1405989175.25048.5.camel@buesod1.americas.hpqcorp.net> Date: Mon, 21 Jul 2014 17:32:55 -0700 From: Davidlohr Bueso <davidlohr@...com> To: Andy Lutomirski <luto@...capital.net> Cc: Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Darren Hart <dvhart@...ux.intel.com>, Andi Kleen <andi@...stfloor.org>, Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...nel.org>, 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> Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex On Mon, 2014-07-21 at 14:31 -0700, Andy Lutomirski wrote: > On Mon, Jul 21, 2014 at 2:27 PM, Peter Zijlstra <peterz@...radead.org> wrote: > > All this is predicated on the fact that syscalls are 'expensive'. > > Weren't syscalls only 100s of cycles? All this bitmap mucking is far > > more expensive due to cacheline misses, which due to the size of the > > things is almost guaranteed. > > 120 - 300 cycles for me, unless tracing happens, and I'm working on > reducing the incidence of tracing. fwiw here's what lmbench's lat_ctx says on my system . For 'accuracy', I kept the runs short. http://www.stgolabs.net/lat_ctx.png -- 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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