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>,
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Subject: Re: [PATCH v2 2/9] x86: numa: check the node id consistently for x86
Date: Mon, 2 Sep 2019 20:25:24 +0800 [thread overview]
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 other threads:[~2019-09-02 12:26 UTC|newest]
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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