linux-kernel - Re: [PATCH v4 2/2] sched/topology: Improve load balancing on AMD EPYC

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Date:   Wed, 9 Oct 2019 05:39:13 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        Rik van Riel <riel@...riel.com>,
        Suravee.Suthikulpanit@....com, Borislav Petkov <bp@...en8.de>,
        Thomas.Lendacky@....com, Mel Gorman <mgorman@...hsingularity.net>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v4 2/2] sched/topology: Improve load balancing on AMD EPYC

On 10/9/19 5:04 AM, Matt Fleming wrote:
> On Mon, 07 Oct, at 08:28:16AM, Guenter Roeck wrote:
>>
>> This patch causes build errors on systems where NUMA does not depend on SMP,
>> for example MIPS and PPC. For example, building mips:ip27_defconfig with SMP
>> disabled results in
>>
>> mips-linux-ld: mm/page_alloc.o: in function `get_page_from_freelist':
>> page_alloc.c:(.text+0x5018): undefined reference to `node_reclaim_distance'
>> mips-linux-ld: page_alloc.c:(.text+0x5020): undefined reference to `node_reclaim_distance'
>> mips-linux-ld: page_alloc.c:(.text+0x5028): undefined reference to `node_reclaim_distance'
>> mips-linux-ld: page_alloc.c:(.text+0x5040): undefined reference to `node_reclaim_distance'
>> Makefile:1074: recipe for target 'vmlinux' failed
>> make: *** [vmlinux] Error 1
>>
>> I have seen a similar problem with one of my PPC test builds.
>>
>> powerpc64-linux-ld: mm/page_alloc.o:(.toc+0x18): undefined reference to `node_reclaim_distance'
> 
> Thanks for this Guenter.
> 
> So, the way I've fixed this same issue for ia64 was to make NUMA
> depend on SMP. Does that seem like a suitable solution for both PPC
> and MIPS?
> 

You would still have to cover all other architectures where SMP and NUMA are independent
of each other. Fortunately, it looks like this is only sh4.

sh4-linux-ld: mm/page_alloc.o: in function `get_page_from_freelist':
page_alloc.c:(.text+0x3ce0): undefined reference to `node_reclaim_distance'
Makefile:1074: recipe for target 'vmlinux' failed
make: *** [vmlinux] Error 1

arm64 and s390 happen to work because they mandate SMP support, even though NUMA
is nominally independent.

Wondering - why not declare node_reclaim_distance outside SMP dependency ?

Thanks,
Guenter