src/patches/suse-2.6.27.39/patches.arch/amd_magny_cour_topology_fix_1.patch

   1 From: Andreas Herrmann <andreas.herrmann3@amd.com>
   2 Subject: x86, sched: Workaround broken sched domain creation for AMD Magny-Cours
   3 References: fate#307306
   4 Patch-Mainline: yes
   5 Commit-ID: 5a925b4282d7f805deafde62001a83dbaf8be275
   6
   7 Signed-off-by: Thomas Renninger <trenn@suse.de>
   8
   9 Current sched domain creation code can't handle multi-node processors.
  10 When switching to power_savings scheduling errors show up and
  11 system might hang later on (due to broken sched domain hierarchy):
  12
  13   # echo 0  >> /sys/devices/system/cpu/sched_mc_power_savings
  14   CPU0 attaching sched-domain:
  15    domain 0: span 0-5 level MC
  16     groups: 0 1 2 3 4 5
  17     domain 1: span 0-23 level NODE
  18      groups: 0-5 6-11 18-23 12-17
  19   ...
  20   # echo 1  >> /sys/devices/system/cpu/sched_mc_power_savings
  21   CPU0 attaching sched-domain:
  22    domain 0: span 0-11 level MC
  23     groups: 0 1 2 3 4 5 6 7 8 9 10 11
  24   ERROR: parent span is not a superset of domain->span
  25     domain 1: span 0-5 level CPU
  26   ERROR: domain->groups does not contain CPU0
  27      groups: 6-11 (__cpu_power = 12288)
  28   ERROR: groups don't span domain->span
  29      domain 2: span 0-23 level NODE
  30       groups:
  31   ERROR: domain->cpu_power not set
  32
  33   ERROR: groups don't span domain->span
  34   ...
  35
  36 Fixing all aspects of power-savings scheduling for Magny-Cours needs
  37 some larger changes in the sched domain creation code.
  38
  39 As a short-term and temporary workaround avoid the problems by
  40 extending "the worst possible hack" ;-(
  41 and always use llc_shared_map on AMD Magny-Cours when MC domain span
  42 is calculated.
  43
  44 With this I get:
  45
  46   # echo 1  >> /sys/devices/system/cpu/sched_mc_power_savings
  47   CPU0 attaching sched-domain:
  48    domain 0: span 0-5 level MC
  49     groups: 0 1 2 3 4 5
  50     domain 1: span 0-5 level CPU
  51      groups: 0-5 (__cpu_power = 6144)
  52      domain 2: span 0-23 level NODE
  53       groups: 0-5 (__cpu_power = 6144) 6-11 (__cpu_power = 6144) 18-23 (__cpu_power = 6144) 12-17 (__cpu_power = 6144)
  54   ...
  55
  56 I.e. no errors during sched domain creation, no system hangs, and also
  57 mc_power_savings scheduling works to a certain extend.
  58
  59 Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
  60 Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
  61 Signed-off-by: H. Peter Anvin <hpa@zytor.com>
  62
  63 ---
  64  arch/x86/kernel/smpboot.c |    3 ++-
  65  1 file changed, 2 insertions(+), 1 deletion(-)
  66
  67 Index: linux-2.6.27-SLE11_BRANCH/arch/x86/kernel/smpboot.c
  68 ===================================================================
  69 --- linux-2.6.27-SLE11_BRANCH.orig/arch/x86/kernel/smpboot.c
  70 +++ linux-2.6.27-SLE11_BRANCH/arch/x86/kernel/smpboot.c
  71 @@ -502,7 +502,8 @@ cpumask_t cpu_coregroup_map(int cpu)
  72          * For perf, we return last level cache shared map.
  73          * And for power savings, we return cpu_core_map
  74          */
  75 -       if (sched_mc_power_savings || sched_smt_power_savings)
  76 +       if ((sched_mc_power_savings || sched_smt_power_savings) &&
  77 +           !(cpu_has(c, X86_FEATURE_AMD_DCM)))
  78                 return per_cpu(cpu_core_map, cpu);
  79         else
  80                 return c->llc_shared_map;