From mboxrd@z Thu Jan 1 00:00:00 1970 From: Davidlohr Bueso Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex Date: Mon, 21 Jul 2014 17:32:55 -0700 Message-ID: <1405989175.25048.5.camel@buesod1.americas.hpqcorp.net> References: <1405956271-34339-1-git-send-email-Waiman.Long@hp.com> <8761iq3bp3.fsf@tassilo.jf.intel.com> <871tte3bjw.fsf@tassilo.jf.intel.com> <20140721212740.GS3935@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-doc-owner@vger.kernel.org To: Andy Lutomirski Cc: Peter Zijlstra , Thomas Gleixner , Darren Hart , Andi Kleen , Waiman Long , Ingo Molnar , Heiko Carstens , "linux-kernel@vger.kernel.org" , Linux API , "linux-doc@vger.kernel.org" , Jason Low , Scott J Norton List-Id: linux-api@vger.kernel.org On Mon, 2014-07-21 at 14:31 -0700, Andy Lutomirski wrote: > On Mon, Jul 21, 2014 at 2:27 PM, Peter Zijlstra 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