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From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
To: Nick Connolly <nick.connolly@mayadata.io>
Cc: dev@dpdk.org, nicolas.dichtel@6wind.com, stable@dpdk.org
Subject: Re: [dpdk-stable] [PATCH] mem: fix allocation failure on non-NUMA kernel
Date: Thu, 17 Sep 2020 15:07:12 +0100
Message-ID: <2ea114be-d606-229c-4fc0-bac06c0ea2fd@intel.com> (raw)
In-Reply-To: <eba65564-e165-ddb0-e260-c8dbff4e675e@mayadata.io>

On 17-Sep-20 2:05 PM, Nick Connolly wrote:
> Hi Anatoly,
> 
> Thanks.  My recollection is that all of the NUMA configuration flags 
> were set to 'n'.
> 
> Regards,
> Nick
> 
> On 17/09/2020 13:57, Burakov, Anatoly wrote:
>> On 17-Sep-20 1:29 PM, Nick Connolly wrote:
>>> Hi Anatoly,
>>>
>>> Thanks for the response.  You are asking a good question - here's 
>>> what I know:
>>>
>>> The issue arose on a single socket system, running WSL2 (full Linux 
>>> kernel running as a lightweight VM under Windows).
>>> The default kernel in this environment is built with CONFIG_NUMA=n 
>>> which means get_mempolicy() returns an error.
>>> This causes the check to ensure that the allocated memory is 
>>> associated with the correct socket to fail.
>>>
>>> The change is to skip the allocation check if check_numa() indicates 
>>> that NUMA-aware memory is not supported.
>>>
>>> Researching the meaning of CONFIG_NUMA, I found 
>>> https://cateee.net/lkddb/web-lkddb/NUMA.html which says:
>>>> Enable NUMA (Non-Uniform Memory Access) support.
>>>> The kernel will try to allocate memory used by a CPU on the local 
>>>> memory controller of the CPU and add some more NUMA awareness to the 
>>>> kernel.
>>>
>>> Clearly CONFIG_NUMA enables memory awareness, but there's no 
>>> indication in the description whether information about the NUMA 
>>> physical architecture is 'hidden', or whether it is still exposed 
>>> through /sys/devices/system/node* (which is used by the rte 
>>> initialisation code to determine how many sockets there are). 
>>> Unfortunately, I don't have ready access to a multi-socket Linux 
>>> system that I can test this out on, so I took the conservative 
>>> approach that it may be possible to have CONFIG_NUMA disabled, but 
>>> the kernel still report more than one node, and coded the change to 
>>> generate a debug message if this occurs.
>>>
>>> Do you know whether CONFIG_NUMA turns off all knowledge about the 
>>> hardware architecture?  If it does, then I agree that the test for 
>>> rte_socket_count() serves no purpose and should be removed.
>>>
>>
>> I have a system with a custom compiled kernel, i can recompile it 
>> without this flag and test this. I'll report back with results :)
>>
> 

With CONFIG_NUMA set to 'n':

[root@xxx ~]# find /sys -name "node*"
/sys/kernel/software_nodes/node0
[root@xxx ~]#

This is confirmed by running DPDK on that machine - i can see all cores 
from all sockets, but they're all appearing on socket 0. So, yes, that 
check isn't necessary :)

-- 
Thanks,
Anatoly

  reply	other threads:[~2020-09-17 14:10 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-05 12:26 Nick Connolly
2020-08-05 13:42 ` Nicolas Dichtel
2020-08-05 14:20   ` Nick Connolly
2020-08-05 14:36     ` Nicolas Dichtel
2020-08-05 14:53       ` Nick Connolly
2020-08-05 15:13         ` Nicolas Dichtel
2020-08-05 15:21           ` Nick Connolly
2020-09-17 11:28             ` Burakov, Anatoly
2020-09-17 11:31 ` Burakov, Anatoly
2020-09-17 12:29   ` Nick Connolly
2020-09-17 12:57     ` Burakov, Anatoly
2020-09-17 13:05       ` Nick Connolly
2020-09-17 14:07         ` Burakov, Anatoly [this message]
2020-09-17 14:08           ` Nick Connolly
2020-09-17 14:18             ` Burakov, Anatoly
2020-09-17 14:19               ` Nick Connolly
2020-10-12 19:28 ` [dpdk-stable] [PATCH v2] " Nick Connolly
2020-10-13  7:59   ` Nicolas Dichtel
2020-10-13 12:01     ` David Marchand

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