[RFC PATCH v2 3/6] sched: pack small tasks

[Mike Galbraith]

On Fri, 2012-12-14 at 14:36 +0800, Alex Shi wrote: 
> On 12/14/2012 12:45 PM, Mike Galbraith wrote:
> >> > Do you have further ideas for buddy cpu on such example?
> >>> > > 
> >>> > > Which kind of sched_domain configuration have you for such system ?
> >>> > > and how many sched_domain level have you ?
> >> > 
> >> > it is general X86 domain configuration. with 4 levels,
> >> > sibling/core/cpu/numa.
> > CPU is a bug that slipped into domain degeneration.  You should have
> > SIBLING/MC/NUMA (chasing that down is on todo).
> 
> Maybe.
> the CPU/NUMA is different on domain flags, CPU has SD_PREFER_SIBLING.

What I noticed during (an unrelated) bisection on a 40 core box was
domains going from so..

3.4.0-bisect (virgin)
[    5.056214] CPU0 attaching sched-domain:
[    5.065009]  domain 0: span 0,32 level SIBLING
[    5.075011]   groups: 0 (cpu_power = 589) 32 (cpu_power = 589)
[    5.088381]   domain 1: span 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76 level MC
[    5.107669]    groups: 0,32 (cpu_power = 1178)  4,36 (cpu_power = 1178)  8,40 (cpu_power = 1178) 12,44 (cpu_power = 1178)
                         16,48 (cpu_power = 1177) 20,52 (cpu_power = 1178) 24,56 (cpu_power = 1177) 28,60 (cpu_power = 1177)
                         64,72 (cpu_power = 1176) 68,76 (cpu_power = 1176)
[    5.162115]    domain 2: span 0-79 level NODE
[    5.171927]     groups: 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76 (cpu_power = 11773)
                           1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61,65,69,73,77 (cpu_power = 11772)
                           2,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,66,70,74,78 (cpu_power = 11773)
                           3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,63,67,71,75,79 (cpu_power = 11770)

..to so, which looks a little bent.  CPU and MC have identical spans, so
CPU should have gone away, as it used to do.

3.6.0-bisect (virgin)
[    3.978338] CPU0 attaching sched-domain:
[    3.987125]  domain 0: span 0,32 level SIBLING
[    3.997125]   groups: 0 (cpu_power = 588) 32 (cpu_power = 589)
[    4.010477]   domain 1: span 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76 level MC
[    4.029748]    groups: 0,32 (cpu_power = 1177)  4,36 (cpu_power = 1177)  8,40 (cpu_power = 1178) 12,44 (cpu_power = 1178)
                         16,48 (cpu_power = 1178) 20,52 (cpu_power = 1178) 24,56 (cpu_power = 1178) 28,60 (cpu_power = 1178)
                         64,72 (cpu_power = 1178) 68,76 (cpu_power = 1177)
[    4.084143]    domain 2: span 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76 level CPU
[    4.103796]     groups: 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76 (cpu_power = 11777)
[    4.124373]     domain 3: span 0-79 level NUMA
[    4.134369]      groups: 0,4,8,12,16,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76 (cpu_power = 11777)
                            1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61,65,69,73,77 (cpu_power = 11778)
                            2,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,66,70,74 ,78 (cpu_power = 11778)
                            3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,63,67,71,75,79 (cpu_power = 11780)

	-Mike