Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology

From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: lvenanci@redhat.com, linux-kernel@vger.kernel.org,
	lwang@redhat.com, Mike Galbraith <efault@gmx.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology
Date: Fri, 14 Apr 2017 12:48:05 +0200	[thread overview]
Message-ID: <20170414104805.lwpo6ywkdrtflkx3@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1492126685.8850.189.camel@redhat.com>

On Thu, Apr 13, 2017 at 07:38:05PM -0400, Rik van Riel wrote:

> What do the sched groups look like for these topologies,
> before and after your patch series?
> 
> > 4 nodes, ring topology
> > node distances:
> > node   0   1   2   3
> >   0:  10  20  30  20
> >   1:  20  10  20  30
> >   2:  30  20  10  20
> >   3:  20  30  20  10

kvm -smp 4 -m 4G -display none -monitor null -serial stdio -kernel
defconfig-build/arch/x86/boot/bzImage -append "sched_debug debug
ignore_loglevel earlyprintk=serial,ttyS0,115200,keep
numa=fake=4:10,20,30,20,20,10,20,30,30,20,10,20,20,30,20,10,0"

(FWIW, that's defconfig+kvmconfig+SCHED_DEBUG=y+NUMA_EMU=y)

Gives me:

[    0.075004] smpboot: Total of 4 processors activated (22345.79 BogoMIPS)
[    0.076767] CPU0 attaching sched-domain:
[    0.077003]  domain 0: span 0-1,3 level NUMA
[    0.078002]   groups: 0 1 3
[    0.079002]   domain 1: span 0-3 level NUMA
[    0.080002]    groups: 0-1,3 (cpu_capacity = 3072) 1-3 (cpu_capacity = 3072)
[    0.081005] CPU1 attaching sched-domain:
[    0.082003]  domain 0: span 0-2 level NUMA
[    0.083002]   groups: 1 2 0
[    0.084002]   domain 1: span 0-3 level NUMA
[    0.085002]    groups: 1-3 (cpu_capacity = 3072) 0-1,3 (cpu_capacity = 3072)
[    0.086004] CPU2 attaching sched-domain:
[    0.087002]  domain 0: span 1-3 level NUMA
[    0.088002]   groups: 2 3 1
[    0.089002]   domain 1: span 0-3 level NUMA
[    0.090002]    groups: 1-3 (cpu_capacity = 3072) 0-1,3 (cpu_capacity = 3072)
[    0.091004] CPU3 attaching sched-domain:
[    0.092002]  domain 0: span 0,2-3 level NUMA
[    0.093002]   groups: 3 0 2
[    0.094002]   domain 1: span 0-3 level NUMA
[    0.095002]    groups: 0-1,3 (cpu_capacity = 3072) 1-3 (cpu_capacity = 3072)
[    0.096004] span: 0-3 (max cpu_capacity = 1024)

With patches it looks like:

[    0.080006] smpboot: Total of 4 processors activated (22345.79 BogoMIPS)
[    0.082545] CPU0 attaching sched-domain:
[    0.083007]  domain 0: span 0-1,3 level NUMA
[    0.084004]   groups: 0 1 3
[    0.085004]   domain 1: span 0-3 level NUMA
[    0.086004]    groups: 0-1,3 (cpu_capacity = 3072) 1-3 (cpu_capacity = 3072)
[    0.087007] CPU1 attaching sched-domain:
[    0.088004]  domain 0: span 0-2 level NUMA
[    0.089004]   groups: 1 0 2
[    0.090004]   domain 1: span 0-3 level NUMA
[    0.091003]    groups: 0-2 (cpu_capacity = 3072) 0,2-3 (cpu_capacity = 3072)
[    0.092008] CPU2 attaching sched-domain:
[    0.093004]  domain 0: span 1-3 level NUMA
[    0.094004]   groups: 2 1 3
[    0.095004]   domain 1: span 0-3 level NUMA
[    0.096004]    groups: 1-3 (cpu_capacity = 3072) 0-1,3 (cpu_capacity = 3072)
[    0.097007] CPU3 attaching sched-domain:
[    0.098004]  domain 0: span 0,2-3 level NUMA
[    0.099003]   groups: 3 0 2
[    0.100004]   domain 1: span 0-3 level NUMA
[    0.101003]    groups: 0,2-3 (cpu_capacity = 3072) 0-2 (cpu_capacity = 3072)
[    0.102007] span: 0-3 (max cpu_capacity = 1024)

Now let me try and reverse engineer those patches ..