From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <45E8BA31.3050808@google.com> Date: Fri, 02 Mar 2007 15:58:41 -0800 From: "Martin J. Bligh" MIME-Version: 1.0 Subject: Re: The performance and behaviour of the anti-fragmentation related patches References: <20070301101249.GA29351@skynet.ie> <20070301160915.6da876c5.akpm@linux-foundation.org> <45E7835A.8000908@in.ibm.com> <20070301195943.8ceb221a.akpm@linux-foundation.org> <20070302162023.GA4691@linux.intel.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Mark Gross , Andrew Morton , Balbir Singh , Mel Gorman , npiggin@suse.de, clameter@engr.sgi.com, mingo@elte.hu, jschopp@austin.ibm.com, arjan@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: > .. and think about a realistic future. > > EVERYBODY will do on-die memory controllers. Yes, Intel doesn't do it > today, but in the one- to two-year timeframe even Intel will. > > What does that mean? It means that in bigger systems, you will no longer > even *have* 8 or 16 banks where turning off a few banks makes sense. > You'll quite often have just a few DIMM's per die, because that's what you > want for latency. Then you'll have CSI or HT or another interconnect. > > And with a few DIMM's per die, you're back where even just 2-way > interleaving basically means that in order to turn off your DIMM, you > probably need to remove HALF the memory for that CPU. > > In other words: TURNING OFF DIMM's IS A BEDTIME STORY FOR DIMWITTED > CHILDREN. Even with only 4 banks per CPU, and 2-way interleaving, we could still power off half the DIMMs in the system. That's a huge impact on the power budget for a large cluster. No, it's not ideal, but what was that quote again ... "perfect is the enemy of good"? Something like that ;-) > There are maybe a couple machines IN EXISTENCE TODAY that can do it. But > nobody actually does it in practice, and nobody even knows if it's going > to be viable (yes, DRAM takes energy, but trying to keep memory free will > likely waste power *too*, and I doubt anybody has any real idea of how > much any of this would actually help in practice). Batch jobs across clusters have spikes at different times of the day, etc that are fairly predictable in many cases. M. -- 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