Re: [rfc][patch] select_idle_sibling() inducing bouncing on westmere

[Mike Galbraith <efault@gmx.de>]

On Sat, 2012-05-26 at 09:29 +0200, Peter Zijlstra wrote: 
> On Sat, 2012-05-26 at 08:37 +0200, Mike Galbraith wrote:
> 
> > Ew. 3.4 went broke for Q6600, and performance went... far far away.
> > 
> > [    0.200057] CPU0 attaching sched-domain:
> > [    0.204016]  domain 0: span 0-3 level MC
> > [    0.208015]   groups: 0 1 2 3
> > [    0.210970] CPU1 attaching sched-domain:
> > [    0.212014]  domain 0: span 0-3 level MC
> > [    0.216016]   groups: 1 2 3 0
> > [    0.220016] CPU2 attaching sched-domain:
> > [    0.224015]  domain 0: span 0-3 level MC
> > [    0.228016]   groups: 2 3 0 1
> > [    0.232015] CPU3 attaching sched-domain:
> > [    0.236016]  domain 0: span 0-3 level MC
> > [    0.240017]   groups: 3 0 1 2
> 
> 
> Oh yikes, I guess I wrecked
> arch/x86/kernel/smpboot.c:cpu_coregroup_mask() in
> 8e7fbcbc22c12414bcc9dfdd683637f58fb32759.
> 
> That should very much always return llc mask, I just got that AMD case
> confused. It looks like it should look like:
> 
> 
> const struct cpumask *cpu_coregroup_mask(int cpu)
> {
> 	return cpu_llc_mask(cpu);
> }

All better.

Too bad 'enterprise dude' turned cpuhog at 3.0, 'silly tester guy' would
have spotted this instantly.  Hohum, back to finding out what happened
to cpufreq.

[    0.212062] CPU0 attaching sched-domain:
[    0.216016]  domain 0: span 0-1 level MC
[    0.220013]   groups: 0 1
[    0.222664]   domain 1: span 0-3 level CPU
[    0.225754]    groups: 0-1 (cpu_power = 2048) 2-3 (cpu_power = 2048)
[    0.233859] CPU1 attaching sched-domain:
[    0.236015]  domain 0: span 0-1 level MC
[    0.241673]   groups: 1 0
[    0.244385]   domain 1: span 0-3 level CPU
[    0.248016]    groups: 0-1 (cpu_power = 2048) 2-3 (cpu_power = 2048)
[    0.254219] CPU2 attaching sched-domain:
[    0.256016]  domain 0: span 2-3 level MC
[    0.261673]   groups: 2 3
[    0.264578]   domain 1: span 0-3 level CPU
[    0.268016]    groups: 2-3 (cpu_power = 2048) 0-1 (cpu_power = 2048)
[    0.276020] CPU3 attaching sched-domain:
[    0.279929]  domain 0: span 2-3 level MC
[    0.281675]   groups: 3 2
[    0.284577]   domain 1: span 0-3 level CPU
[    0.289764]    groups: 2-3 (cpu_power = 2048) 0-1 (cpu_power = 2048)