From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86F7CC433F5 for ; Wed, 9 Feb 2022 10:15:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230234AbiBIKPW (ORCPT ); Wed, 9 Feb 2022 05:15:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54298 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229545AbiBIKPU (ORCPT ); Wed, 9 Feb 2022 05:15:20 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64619E04A3C2; Wed, 9 Feb 2022 02:11:52 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 34786CE1F47; Wed, 9 Feb 2022 10:10:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06712C340E9; Wed, 9 Feb 2022 10:10:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644401414; bh=5AvWakUZDtNEGqIlDbVrB5adlg1oKtLY8vuvEfAL8pY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Ra2xlVjoULi2O/4ZDQj8zIO0CpanWvdruq6MGNyQ9qoXaHsDBTqHycIv/MN5Sdst+ rhk0/PXscdxhoimIkgtTzIhwRW2v/iQrvytSuYUuYxVVgINwhyPsdeRyWb+9YkdWdB pM63UROPza7oLFC1z/+wxaA/Wghmar2fHUbFOMMBa/iUYVORzAiSXtJMgSv7HZBoiz zp6SG3NmyzVYetIsN/UftGZO8si/Bl0cUBya2c1MZVgEQLhgu04NcMnDYw7dWNvK8t kbRDM4sWisL/NRd90IPOT1VHnCl/wbxW9W53WiJNPPtZWH8FpH0ALh83zd+5+LboC9 Igc6nN4z+j3MQ== Date: Wed, 9 Feb 2022 12:10:07 +0200 From: Leon Romanovsky To: Tony Lu Cc: Stefan Raspl , kgraul@linux.ibm.com, kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, RDMA mailing list Subject: Re: [PATCH net-next] net/smc: Allocate pages of SMC-R on ibdev NUMA node Message-ID: References: <20220130190259.94593-1-tonylu@linux.alibaba.com> <6d88abaa-62b8-c2ae-2b96-ceca6eea28e7@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Feb 09, 2022 at 04:00:34PM +0800, Tony Lu wrote: > On Tue, Feb 08, 2022 at 11:32:23AM +0200, Leon Romanovsky wrote: > > On Tue, Feb 08, 2022 at 10:10:55AM +0100, Stefan Raspl wrote: > > > On 2/7/22 14:49, Leon Romanovsky wrote: > > > > On Mon, Feb 07, 2022 at 05:59:58PM +0800, Tony Lu wrote: > > > > > On Mon, Jan 31, 2022 at 09:20:52AM +0200, Leon Romanovsky wrote: > > > > > > On Mon, Jan 31, 2022 at 03:03:00AM +0800, Tony Lu wrote: > > > > > > > Currently, pages are allocated in the process context, for its NUMA node > > > > > > > isn't equal to ibdev's, which is not the best policy for performance. > > > > > > > > > > > > > > Applications will generally perform best when the processes are > > > > > > > accessing memory on the same NUMA node. When numa_balancing enabled > > > > > > > (which is enabled by most of OS distributions), it moves tasks closer to > > > > > > > the memory of sndbuf or rmb and ibdev, meanwhile, the IRQs of ibdev bind > > > > > > > to the same node usually. This reduces the latency when accessing remote > > > > > > > memory. > > > > > > > > > > > > It is very subjective per-specific test. I would expect that > > > > > > application will control NUMA memory policies (set_mempolicy(), ...) > > > > > > by itself without kernel setting NUMA node. > > > > > > > > > > > > Various *_alloc_node() APIs are applicable for in-kernel allocations > > > > > > where user can't control memory policy. > > > > > > > > > > > > I don't know SMC-R enough, but if I judge from your description, this > > > > > > allocation is controlled by the application. > > > > > > > > > > The original design of SMC doesn't handle the memory allocation of > > > > > different NUMA node, and the application can't control the NUMA policy > > > > > in SMC. > > > > > > > > > > It allocates memory according to the NUMA node based on the process > > > > > context, which is determined by the scheduler. If application process > > > > > runs on NUMA node 0, SMC allocates on node 0 and so on, it all depends > > > > > on the scheduler. If RDMA device is attached to node 1, the process runs > > > > > on node 0, it allocates memory on node 0. > > > > > > > > > > This patch tries to allocate memory on the same NUMA node of RDMA > > > > > device. Applications can't know the current node of RDMA device. The > > > > > scheduler knows the node of memory, and can let applications run on the > > > > > same node of memory and RDMA device. > > > > > > > > I don't know, everything explained above is controlled through memory > > > > policy, where application needs to run on same node as ibdev. > > > > > > The purpose of SMC-R is to provide a drop-in replacement for existing TCP/IP > > > applications. The idea is to avoid almost any modification to the > > > application, just switch the address family. So while what you say makes a > > > lot of sense for applications that intend to use RDMA, in the case of SMC-R > > > we can safely assume that most if not all applications running it assume > > > they get connectivity through a non-RDMA NIC. Hence we cannot expect the > > > applications to think about aspects such as NUMA, and we should do the right > > > thing within SMC-R. > > > > And here comes the problem, you are doing the right thing for very > > specific and narrow use case, where application and ibdev run on > > same node. It is not true for multi-core systems as application will > > be scheduled on less load node (in very simplistic form). > > > > In general case, the application will get CPU and memory based on scheduler > > heuristic as you don't use memory policy to restrict it. The assumption > > that allocations need to be close to ibdev and not to applications can > > lead to worse performance. > > > > Yes, the applications cannot run faster if they always access remote > memory. There are something complex in SMC, so choose to bind to the > RDMA device. > > As Stefan mentioned, SMC is to provide a drop-in replacement for TCP. If I'm looking on the right piece of code (net/core/skbuff.c:build_skb), even SKB is not allocated close to ehternet device. I'm not convinced that SMC should be different here. Thanks