linux-kernel - Re: [PATCH] cpu-topology: warn if NUMA configurations conflicts with lower layer

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Message-ID: <15050bf2-99ec-e604-ab95-827ce86fd693@arm.com>
Date:   Mon, 13 Jan 2020 11:16:46 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     "Zengtao (B)" <prime.zeng@...ilicon.com>,
        Morten Rasmussen <morten.rasmussen@....com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Linuxarm <linuxarm@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpu-topology: warn if NUMA configurations conflicts with
 lower layer

On 13/01/2020 06:51, Zengtao (B) wrote:
> I have tried both, this previous one don't work. But this one seems work
> correctly with the warning message printout as expected.
> 

Thanks for trying it out.

> This patch is based on the fact " non-NUMA spans shouldn't overlap ", I am
> not quite sure if this is always true? 
> 

I think this is required for get_group() to work properly. Otherwise,
successive get_group() calls may override (and break) the sd->groups
linking as you initially reported.

In your example, for MC level we have

  tl->mask(3) == 3-7
  tl->mask(4) == 4-7

Which partially overlaps, causing the relinking of '7->3' to '7->4'. Valid
configurations would be

  wholly disjoint:
  tl->mask(3) == 0-3
  tl->maks(4) == 4-7

  equal:
  tl->mask(3) == 3-7
  tl->mask(4) == 3-7

> Anyway, Could you help to raise the new patch?
> 

Ideally I'd like to be able to reproduce this locally first (TBH I'd like
to get my first suggestion to work since it's less intrusive). Could you
share how you were able to trigger this? Dietmar's been trying to reproduce
this with qemu but I don't think he's there just yet.

> Thanks
> Zengtao
> 
>>
>>> Thanks
>>> Zengtao
>>>
>>>>
>>>> Morten