From: Yunsheng Lin <linyunsheng@huawei.com> To: Peter Zijlstra <peterz@infradead.org> Cc: <dalias@libc.org>, <linux-sh@vger.kernel.org>, <catalin.marinas@arm.com>, <dave.hansen@linux.intel.com>, <heiko.carstens@de.ibm.com>, <linuxarm@huawei.com>, <jiaxun.yang@flygoat.com>, <linux-kernel@vger.kernel.org>, <mwb@linux.vnet.ibm.com>, <paulus@samba.org>, <hpa@zytor.com>, <sparclinux@vger.kernel.org>, <chenhc@lemote.com>, <will@kernel.org>, <linux-s390@vger.kernel.org>, <ysato@users.sourceforge.jp>, <mpe@ellerman.id.au>, <x86@kernel.org>, <rppt@linux.ibm.com>, <borntraeger@de.ibm.com>, <dledford@redhat.com>, <mingo@redhat.com>, <jeffrey.t.kirsher@intel.com>, <benh@kernel.crashing.org>, <jhogan@kernel.org>, <nfont@linux.vnet.ibm.com>, <mattst88@gmail.com>, <len.brown@intel.com>, <gor@linux.ibm.com>, <anshuman.khandual@arm.com>, <ink@jurassic.park.msu.ru>, <cai@lca.pw>, <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>, <robin.murphy@arm.com>, <linux-mips@vger.kernel.org>, <ralf@linux-mips.org>, <tbogendoerfer@suse.de>, <paul.burton@mips.com>, <linux-alpha@vger.kernel.org>, <bp@alien8.de>, <akpm@linux-foundation.org>, <linuxppc-dev@lists.ozlabs.org>, <davem@davemloft.net> Subject: Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86 Date: Mon, 2 Sep 2019 20:25:24 +0800 Message-ID: <5fa2aa99-89fa-cd41-b090-36a23cfdeb73@huawei.com> (raw) In-Reply-To: <20190902072542.GN2369@hirez.programming.kicks-ass.net> On 2019/9/2 15:25, Peter Zijlstra wrote: > On Mon, Sep 02, 2019 at 01:46:51PM +0800, Yunsheng Lin wrote: >> On 2019/9/1 0:12, Peter Zijlstra wrote: > >>> 1) because even it is not set, the device really does belong to a node. >>> It is impossible a device will have magic uniform access to memory when >>> CPUs cannot. >> >> So it means dev_to_node() will return either NUMA_NO_NODE or a >> valid node id? > > NUMA_NO_NODE := -1, which is not a valid node number. It is also, like I > said, not a valid device location on a NUMA system. > > Just because ACPI/BIOS is shit, doesn't mean the device doesn't have a > node association. It just means we don't know and might have to guess. How do we guess the device's location when ACPI/BIOS does not set it? It seems dev_to_node() does not do anything about that and leave the job to the caller or whatever function that get called with its return value, such as cpumask_of_node(). > >>> 2) is already true today, cpumask_of_node() requires a valid node_id. >> >> Ok, most of the user does check node_id before calling >> cpumask_of_node(), but does a little different type of checking: >> >> 1) some does " < 0" check; >> 2) some does "== NUMA_NO_NODE" check; >> 3) some does ">= MAX_NUMNODES" check; >> 4) some does "< 0 || >= MAX_NUMNODES || !node_online(node)" check. > > The one true way is: > > '(unsigned)node_id >= nr_node_ids' I missed the magic of the "unsigned" in your previous reply. > >>> 3) is just wrong and increases overhead for everyone. >> >> Ok, cpumask_of_node() is also used in some critical path such >> as scheduling, which may not need those checking, the overhead >> is unnecessary. >> >> But for non-critical path such as setup or configuration path, >> it better to have consistent checking, and also simplify the >> user code that calls cpumask_of_node(). >> >> Do you think it is worth the trouble to add a new function >> such as cpumask_of_node_check(maybe some other name) to do >> consistent checking? >> >> Or caller just simply check if dev_to_node()'s return value is >> NUMA_NO_NODE before calling cpumask_of_node()? > > It is not a matter of convenience. The function is called > cpumask_of_node(), when node < 0 || node >= nr_node_ids, it is not a > valid node, therefore the function shouldn't return anything except an > error. what do you mean by error? What I can think is three type of errors: 1) return NULL, this way it seems cpumask_of_node() also leave the job to the function that calls it. 2) cpu_none_mask, I am not sure what this means, maybe it means there is no cpu on the same node with the device? 3) give a warning, stack dump, or even a BUG_ON? I would prefer the second one, and implement the third one when the CONFIG_DEBUG_PER_CPU_MAPS is selected. Any suggestion? > > Also note that the CONFIG_DEBUG_PER_CPU_MAPS version of > cpumask_of_node() already does this (although it wants the below fix). Thanks for the note and example.
next prev parent reply index Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-31 5:58 [PATCH v2 0/9] check the node id consistently across different arches Yunsheng Lin 2019-08-31 5:58 ` [PATCH v2 1/9] arm64: numa: check the node id consistently for arm64 Yunsheng Lin 2019-08-31 5:58 ` [PATCH v2 2/9] x86: numa: check the node id consistently for x86 Yunsheng Lin 2019-08-31 8:55 ` Peter Zijlstra 2019-08-31 10:09 ` Yunsheng Lin 2019-08-31 16:12 ` Peter Zijlstra 2019-09-01 4:45 ` Something about loongson_llsc_mb 陈华才 [not found] ` <2019090410032559707512@loongson.cn> 2019-09-04 9:21 ` Peter Zijlstra 2019-09-04 10:04 ` Peter Zijlstra 2019-09-04 12:57 ` Huang Pei 2019-09-02 5:46 ` [PATCH v2 2/9] x86: numa: check the node id consistently for x86 Yunsheng Lin 2019-09-02 7:25 ` Peter Zijlstra 2019-09-02 12:25 ` Yunsheng Lin [this message] 2019-09-02 12:56 ` Peter Zijlstra 2019-09-02 18:22 ` Ingo Molnar 2019-09-02 19:14 ` Peter Zijlstra 2019-09-03 6:19 ` Yunsheng Lin 2019-09-03 7:11 ` Peter Zijlstra 2019-09-03 8:31 ` Yunsheng Lin 2019-09-02 18:17 ` Ingo Molnar 2019-09-03 7:53 ` [PATCH] x86/mm: Fix cpumask_of_node() error condition Peter Zijlstra 2019-08-31 5:58 ` [PATCH v2 3/9] alpha: numa: check the node id consistently for alpha Yunsheng Lin 2019-08-31 5:58 ` [PATCH v2 4/9] powerpc: numa: check the node id consistently for powerpc Yunsheng Lin 2019-08-31 5:58 ` [PATCH v2 5/9] s390: numa: check the node id consistently for s390 Yunsheng Lin 2019-09-02 4:05 ` kbuild test robot 2019-08-31 5:58 ` [PATCH v2 6/9] sh: numa: check the node id consistently for sh Yunsheng Lin 2019-08-31 5:58 ` [PATCH v2 7/9] sparc64: numa: check the node id consistently for sparc64 Yunsheng Lin 2019-08-31 6:53 ` David Miller 2019-08-31 8:57 ` Yunsheng Lin 2019-08-31 20:02 ` David Miller 2019-09-02 6:08 ` Yunsheng Lin 2019-09-02 15:17 ` David Miller 2019-08-31 5:58 ` [PATCH v2 8/9] mips: numa: check the node id consistently for mips ip27 Yunsheng Lin 2019-08-31 5:58 ` [PATCH v2 9/9] mips: numa: check the node id consistently for mips loongson64 Yunsheng Lin
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