linux-kernel - Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <8cff8350-311e-3817-0c42-b6f98de589a3@huawei.com>
Date:   Tue, 24 Sep 2019 19:44:28 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Michal Hocko <mhocko@...nel.org>, <catalin.marinas@....com>,
        <will@...nel.org>, <mingo@...hat.com>, <bp@...en8.de>,
        <rth@...ddle.net>, <ink@...assic.park.msu.ru>,
        <mattst88@...il.com>, <benh@...nel.crashing.org>,
        <paulus@...ba.org>, <mpe@...erman.id.au>,
        <heiko.carstens@...ibm.com>, <gor@...ux.ibm.com>,
        <borntraeger@...ibm.com>, <ysato@...rs.sourceforge.jp>,
        <dalias@...c.org>, <davem@...emloft.net>, <ralf@...ux-mips.org>,
        <paul.burton@...s.com>, <jhogan@...nel.org>,
        <jiaxun.yang@...goat.com>, <chenhc@...ote.com>,
        <akpm@...ux-foundation.org>, <rppt@...ux.ibm.com>,
        <anshuman.khandual@....com>, <tglx@...utronix.de>, <cai@....pw>,
        <robin.murphy@....com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>, <x86@...nel.org>,
        <dave.hansen@...ux.intel.com>, <luto@...nel.org>,
        <len.brown@...el.com>, <axboe@...nel.dk>, <dledford@...hat.com>,
        <jeffrey.t.kirsher@...el.com>, <linux-alpha@...r.kernel.org>,
        <naveen.n.rao@...ux.vnet.ibm.com>, <mwb@...ux.vnet.ibm.com>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-s390@...r.kernel.org>,
        <linux-sh@...r.kernel.org>, <sparclinux@...r.kernel.org>,
        <tbogendoerfer@...e.de>, <linux-mips@...r.kernel.org>,
        <rafael@...nel.org>, <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware

On 2019/9/24 19:28, Peter Zijlstra wrote:
> On Tue, Sep 24, 2019 at 07:07:36PM +0800, Yunsheng Lin wrote:
>> On 2019/9/24 17:25, Peter Zijlstra wrote:
>>> 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.
>>
>> Not really.
>> For packet sending and receiving, the buffer memory may be allocated
>> dynamically. Node of tx buffer memory is mainly based on the cpu
>> that is sending sending, node of rx buffer memory is mainly based on
>> the cpu the interrupt handler of the device is running on, and the
>> device' interrupt affinity is mainly based on node id of the device.
>>
>> We can bind the processes that are using the device to both nodes
>> in order to utilize memory on both nodes for packet sending.
>>
>> But for packet receiving, the node1 may not be used becuase the node
>> id of device is forced to node 0, which is the default way to bind
>> the interrupt to the cpu of the same node.
>>
>> If node_to_cpumask_map() returns all usable cpus when the device's node
>> id is NUMA_NO_NODE, then interrupt can be binded to the cpus on both nodes.
> 
> s/binded/bound/
> 
> Sure; the data can be allocated wherever, but the control structures are
> not dynamically allocated every time. They are persistent, and they will
> be local to some node.
> 
> Anyway, are you saying this stupid corner case is actually relevant?
> Because how does it scale out? What if you have 8 sockets, with each
> socket having 2 nodes and 1 such magic device. Then returning all CPUs
> is just plain wrong.

Yes, the hardware may not scale out, but what about the virtual device?

> 
>>>> 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.
>>
>> There may be similar handling as above for virtual device too.
> 
> And it'd be similarly broken.

>From [1], there is a lot of devices with node id of NUMA_NO_NODE with the
FW_BUG.

[1] https://lore.kernel.org/lkml/5a188e2b-6c07-a9db-fbaa-561e9362d3ba@huawei.com/


> 
> .
>