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From: Peter Zijlstra <peterz@infradead.org>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: dalias@libc.org, linux-sh@vger.kernel.org,
	catalin.marinas@arm.com, dave.hansen@linux.intel.com,
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	davem@davemloft.net,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86
Date: Tue, 3 Sep 2019 09:11:11 +0200
Message-ID: <20190903071111.GU2369@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1f48081c-c9d6-8f3e-9559-8b0bec98f125@huawei.com>

On Tue, Sep 03, 2019 at 02:19:04PM +0800, Yunsheng Lin wrote:
> On 2019/9/2 20:56, Peter Zijlstra wrote:
> > On Mon, Sep 02, 2019 at 08:25:24PM +0800, Yunsheng Lin wrote:
> >> 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?
> > 
> > See device_add(), it looks to the device's parent and on NO_NODE, puts
> > it there.
> > 
> > Lacking any hints, just stick it to node0 and print a FW_BUG or
> > something.
> > 
> >> 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().
> > 
> > Well, dev_to_node() doesn't do anything; nor should it. It are the
> > callers of set_dev_node() that should be taking care.
> > 
> > Also note how device_add() sets the device node to the parent device's
> > node on NUMA_NO_NODE. Arguably we should change it to complain when it
> > finds NUMA_NO_NODE and !parent.
> 
> Is it possible that the node id set by device_add() become invalid
> if the node is offlined, then dev_to_node() may return a invalid
> node id.

In that case I would expect the device to go away too. Once the memory
controller goes away, the PCI bus connected to it cannot continue to
function.

> From the comment in select_fallback_rq(), it seems that a node can
> be offlined, not sure if node offline process has taken cared of that?
> 
> 	/*
>          * If the node that the CPU is on has been offlined, cpu_to_node()
>          * will return -1. There is no CPU on the node, and we should
>          * select the CPU on the other node.
>          */

Ugh, so I disagree with that notion. cpu_to_node() mapping should be
fixed, you simply cannot change it after boot, too much stuff relies on
it.

Setting cpu_to_node to -1 on node offline is just wrong. But alas, it
seems this is already so.

> With the above assumption that a device is always on a valid node,
> the node id returned from dev_to_node() can be safely passed to
> cpumask_of_node() without any checking?



  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
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 [this message]
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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