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Tue, 24 Sep 2019 11:23:55 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 89B20305E54; Tue, 24 Sep 2019 13:23:03 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 270C220D80D42; Tue, 24 Sep 2019 13:23:49 +0200 (CEST) Date: Tue, 24 Sep 2019 13:23:49 +0200 From: Peter Zijlstra To: Michal Hocko Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware Message-ID: <20190924112349.GJ2332@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> <20190924074751.GB23050@dhcp22.suse.cz> <20190924091714.GJ2369@hirez.programming.kicks-ass.net> <20190924105622.GH23050@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924105622.GH23050@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: dalias@libc.org, linux-sh@vger.kernel.org, catalin.marinas@arm.com, dave.hansen@linux.intel.com, heiko.carstens@de.ibm.com, jiaxun.yang@flygoat.com, linux-mips@vger.kernel.org, mwb@linux.vnet.ibm.com, paulus@samba.org, hpa@zytor.com, sparclinux@vger.kernel.org, chenhc@lemote.com, will@kernel.org, cai@lca.pw, linux-s390@vger.kernel.org, ysato@users.sourceforge.jp, x86@kernel.org, Yunsheng Lin , rppt@linux.ibm.com, borntraeger@de.ibm.com, dledford@redhat.com, mingo@redhat.com, jeffrey.t.kirsher@intel.com, jhogan@kernel.org, mattst88@gmail.com, len.brown@intel.com, gor@linux.ibm.com, anshuman.khandual@arm.com, gregkh@linuxfoundation.org, bp@alien8.de, luto@kernel.org, tglx@linutronix.de, naveen.n.rao@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, rth@twiddle.net, axboe@kernel.dk, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, ralf@linux-mips.org, tbogendoerfer@suse.de, paul.burton@mips.com, linux-alpha@vger.kernel.org, rafael@kernel.org, ink@jurassic.park.msu.ru, akpm@linux-foundation.org, robin.murphy@arm.com, davem@davemloft.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Archived-At: List-Archive: On Tue, Sep 24, 2019 at 12:56:22PM +0200, Michal Hocko wrote: > On Tue 24-09-19 11:17:14, Peter Zijlstra wrote: > > On Tue, Sep 24, 2019 at 09:47:51AM +0200, Michal Hocko wrote: > > > On Mon 23-09-19 22:34:10, Peter Zijlstra wrote: > > > > On Mon, Sep 23, 2019 at 06:52:35PM +0200, Michal Hocko wrote: > > > [...] > > > > > I even the > > > > > ACPI standard is considering this optional. Yunsheng Lin has referred to > > > > > the specific part of the standard in one of the earlier discussions. > > > > > Trying to guess the node affinity is worse than providing all CPUs IMHO. > > > > > > > > I'm saying the ACPI standard is wrong. > > > > > > Even if you were right on this the reality is that a HW is likely to > > > follow that standard and we cannot rule out NUMA_NO_NODE being > > > specified. As of now we would access beyond the defined array and that > > > is clearly a bug. > > > > Right, because the device node is wrong, so we fix _that_! > > > > > Let's assume that this is really a bug for a moment. What are you going > > > to do about that? BUG_ON? I do not really see any solution besides to either > > > provide something sensible or BUG_ON. If you are worried about a > > > conditional then this should be pretty easy to solve by starting the > > > array at -1 index and associate it with the online cpu mask. > > > > The same thing I proposed earlier; force the device node to 0 (or any > > other convenient random valid value) and issue a FW_BUG message to the > > console. > > Why would you "fix" anything and how do you know that node 0 is the > right choice? I have seen setups with node 0 without any memory and > similar unexpected things. We don't know 0 is right; but we know 'unkown' is wrong, so we FW_BUG and pick _something_. > To be honest I really fail to see why to object to a simple semantic > that NUMA_NO_NODE imply all usable cpus. Could you explain that please? Because it feels wrong. The device needs to be _somewhere_. It simply cannot be node-less.