From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f175.google.com (mail-ig0-f175.google.com [209.85.213.175]) by kanga.kvack.org (Postfix) with ESMTP id 750506B006C for ; Thu, 23 Apr 2015 15:25:01 -0400 (EDT) Received: by igbyr2 with SMTP id yr2so33035137igb.0 for ; Thu, 23 Apr 2015 12:25:01 -0700 (PDT) Received: from e39.co.us.ibm.com (e39.co.us.ibm.com. [32.97.110.160]) by mx.google.com with ESMTPS id sd11si139115igb.20.2015.04.23.12.25.00 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 23 Apr 2015 12:25:00 -0700 (PDT) Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 23 Apr 2015 13:25:00 -0600 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id 2BC823E40048 for ; Thu, 23 Apr 2015 13:24:58 -0600 (MDT) Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by b03cxnp08027.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t3NJOwRY26673356 for ; Thu, 23 Apr 2015 12:24:58 -0700 Received: from d03av05.boulder.ibm.com (localhost [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t3NJOvRo002209 for ; Thu, 23 Apr 2015 13:24:57 -0600 Date: Thu, 23 Apr 2015 12:24:56 -0700 From: "Paul E. McKenney" Subject: Re: Interacting with coherent memory on external devices Message-ID: <20150423192456.GQ5561@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150421214445.GA29093@linux.vnet.ibm.com> <20150422000538.GB6046@gmail.com> <20150422131832.GU5561@linux.vnet.ibm.com> <20150422170737.GB4062@gmail.com> <20150422185230.GD5561@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Jerome Glisse , linux-kernel@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, mgorman@suse.de, aarcange@redhat.com, riel@redhat.com, airlied@redhat.com, benh@kernel.crashing.org, aneesh.kumar@linux.vnet.ibm.com, Cameron Buschardt , Mark Hairgrove , Geoffrey Gerfin , John McKenna , akpm@linux-foundation.org On Thu, Apr 23, 2015 at 09:12:38AM -0500, Christoph Lameter wrote: > On Wed, 22 Apr 2015, Paul E. McKenney wrote: > > > Agreed, the use case that Jerome is thinking of differs from yours. > > You would not (and should not) tolerate things like page faults because > > it would destroy your worst-case response times. I believe that Jerome > > is more interested in throughput with minimal change to existing code. > > As far as I know Jerome is talkeing about HPC loads and high performance > GPU processing. This is the same use case. The difference is sensitivity to latency. You have latency-sensitive HPC workloads, and Jerome is talking about HPC workloads that need high throughput, but are insensitive to latency. > > Let's suppose that you and Jerome were using GPGPU hardware that had > > 32,768 hardware threads. You would want very close to 100% of the full > > throughput out of the hardware with pretty much zero unnecessary latency. > > In contrast, Jerome might be OK with (say) 20,000 threads worth of > > throughput with the occasional latency hiccup. > > > > And yes, support for both use cases is needed. > > What you are proposing for High Performacne Computing is reducing the > performance these guys trying to get. You cannot sell someone a Volkswagen > if he needs the Ferrari. You do need the low-latency Ferrari. But others are best served by a high-throughput freight train. Thanx, Paul -- 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