linux-kernel - [bisected] 051f3ca02e46 "Introduce NUMA identity node sched domain" breaks fake NUMA on s390

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Message-Id: <20180512100233.GB3738@osiris>
Date:   Sat, 12 May 2018 12:02:33 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Andre Wild <wild@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org
Subject: [bisected] 051f3ca02e46 "Introduce NUMA identity node sched domain"
 breaks fake NUMA on s390

Hello,

Andre Wild reported that fake NUMA doesn't work on s390 anymore. Doesn't
work means it crashed for Andre, or it is in an endless loop within
init_sched_groups_capacity() for me (sg != sd->groups is always true).

I could reproduce this with a very simple setup with only two nodes, where
each node has only one CPU. This allowed me to bisect it down to commit
051f3ca02e46 ("sched/topology: Introduce NUMA identity node sched domain").

With that commit reverted the system comes up again and the scheduling
domains look like this:

[    0.148592] smp: Bringing up secondary CPUs ...
[    0.148984] smp: Brought up 2 nodes, 2 CPUs
[    0.149097] CPU0 attaching sched-domain(s):
[    0.149099]  domain-0: span=0-1 level=NUMA
[    0.149101]   groups: 0:{ span=0 }, 1:{ span=1 }
[    0.149106] CPU1 attaching sched-domain(s):
[    0.149107]  domain-0: span=0-1 level=NUMA
[    0.149108]   groups: 1:{ span=1 }, 0:{ span=0 }
[    0.149111] span: 0-1 (max cpu_capacity = 1024)

Any idea what's going wrong?

Config file is attached.

Thanks,
Heiko

View attachment "config" of type "text/plain" (76969 bytes)