From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 6 Mar 2006 18:10:02 -0800 From: Benjamin LaHaise Subject: Re: [PATCH] avoid atomic op on page free Message-ID: <20060307021002.GL32565@linux.intel.com> References: <20060307001015.GG32565@linux.intel.com> <20060306165039.1c3b66d8.akpm@osdl.org> <20060307011107.GI32565@linux.intel.com> <440CEA34.1090205@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <440CEA34.1090205@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andrew Morton , linux-mm@kvack.org, netdev@vger.kernel.org List-ID: On Tue, Mar 07, 2006 at 01:04:36PM +1100, Nick Piggin wrote: > I'd say it will turn out to be more trouble than its worth, for the > miserly cost > avoiding one atomic_inc, and one atomic_dec_and_test on page-local data > that will > be in L1 cache. I'd never turn my nose up at anyone just having a go > though :) The cost is anything but miserly. Consider that every lock instruction is a memory barrier which takes your OoO CPU with lots of instructions in flight to ramp down to just 1 for the time it takes that instruction to execute. That synchronization is what makes the atomic expensive. In the case of netperf, I ended up with a 2.5Gbit/s (~30%) performance improvement through nothing but microoptimizations. There is method to my madness. ;-) -ben -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org