From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:46044 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2504189AbfIXJ0r (ORCPT ); Tue, 24 Sep 2019 05:26:47 -0400 Date: Tue, 24 Sep 2019 11:25:51 +0200 From: Peter Zijlstra Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware Message-ID: <20190924092551.GK2369@hirez.programming.kicks-ass.net> References: <1568724534-146242-1-git-send-email-linyunsheng@huawei.com> <20190923151519.GE2369@hirez.programming.kicks-ass.net> <20190923152856.GB17206@dhcp22.suse.cz> <20190923154852.GG2369@hirez.programming.kicks-ass.net> <20190923165235.GD17206@dhcp22.suse.cz> <20190923203410.GI2369@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-s390-owner@vger.kernel.org List-ID: To: Yunsheng Lin Cc: Michal Hocko , catalin.marinas@arm.com, will@kernel.org, mingo@redhat.com, bp@alien8.de, rth@twiddle.net, ink@jurassic.park.msu.ru, mattst88@gmail.com, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, heiko.carstens@de.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, ysato@users.sourceforge.jp, dalias@libc.org, davem@davemloft.net, ralf@linux-mips.org, paul.burton@mips.com, jhogan@kernel.org, jiaxun.yang@flygoat.com, chenhc@lemote.com, akpm@linux-foundation.org, rppt@linux.ibm.com, anshuman.khandual@arm.com, tglx@linutronix.de, cai@lca.pw, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, hpa@zytor.com, x86@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, len.brown@intel.com, axboe@kernel.dk, dledford@redhat.com, jeffrey.t.kirsher@intel.com, linux-alpha@vger.kernel.org, naveen.n.rao@linux.vnet.ibm.com, mwb@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, tbogendoerfer@suse.de, linux-mips@vger.kernel.org, rafael@kernel.org, gregkh@linuxfoundation.org On Tue, Sep 24, 2019 at 09:29:50AM +0800, Yunsheng Lin wrote: > On 2019/9/24 4:34, Peter Zijlstra wrote: > > I'm saying the ACPI standard is wrong. Explain to me how it is > > physically possible to have a device without NUMA affinity in a NUMA > > system? > > > > 1) The fundamental interconnect is not uniform. > > 2) The device needs to actually be somewhere. > > > > From what I can see, NUMA_NO_NODE may make sense in the below case: > > 1) Theoretically, there would be a device that can access all the memory > uniformly and can be accessed by all cpus uniformly even in a NUMA system. > Suppose we have two nodes, and the device just sit in the middle of the > interconnect between the two nodes. > > Even we define a third node solely for the device, we may need to look at > the node distance to decide the device can be accessed uniformly. > > Or we can decide that the device can be accessed uniformly by setting > it's node to NUMA_NO_NODE. This is indeed a theoretical case; it doesn't scale. The moment you're adding multiple sockets or even board interconnects this all goes out the window. And in this case, forcing the device to either node is fine. > 2) For many virtual deivces, such as tun or loopback netdevice, they > are also accessed uniformly by all cpus. Not true; the virtual device will sit in memory local to some node. And as with physical devices, you probably want at least one (virtual) queue per node.