src/patches/suse-2.6.27.39/patches.arch/s390-05-08-topology.patch

   1 From: Gerald Schaefer <geraldsc@de.ibm.com>
   2 Subject: kernel: disable cpu topology support by default
   3 References: bnc#450096,LTC#50392
   4
   5 Symptom:     System performance may be lower than expected.
   6 Problem:     If the hardware supports the configuration-topology facility
   7              the system cpu topology information will be passed to the
   8              scheduler. The scheduler bases its load balancing decisions
   9              also on the cpu topology. This may have a negative performance
  10              impact on machines where I/O interrupts are distributed unevenly
  11              to cpus. Those cpus which are grouped together and get more I/O
  12              interrupts than others will tend to have a higher average load.
  13 Solution:    Disable cpu topology support by default and add a kernel parameter
  14              which allows to switch it on. In order to switch support on
  15              topology=on needs to be added to the kernel parameter line.
  16
  17 Acked-by: John Jolly <jjolly@suse.de>
  18 ---
  19  Documentation/kernel-parameters.txt |    8 ++++++++
  20  arch/s390/kernel/topology.c         |   12 +++++++++++-
  21  2 files changed, 19 insertions(+), 1 deletion(-)
  22
  23 --- a/Documentation/kernel-parameters.txt
  24 +++ b/Documentation/kernel-parameters.txt
  25 @@ -2201,6 +2201,14 @@ and is between 256 and 4096 characters.
  26                         See comment before function dc390_setup() in
  27                         drivers/scsi/tmscsim.c.
  28
  29 +       topology=       [S390]
  30 +                       Format: {off | on}
  31 +                       Specify if the kernel should make use of the cpu
  32 +                       topology informations if the hardware supports these.
  33 +                       The scheduler will make use of these informations and
  34 +                       e.g. base its process migration decisions on it.
  35 +                       Default is off.
  36 +
  37         tp720=          [HW,PS2]
  38
  39         trix=           [HW,OSS] MediaTrix AudioTrix Pro
  40 --- a/arch/s390/kernel/topology.c
  41 +++ b/arch/s390/kernel/topology.c
  42 @@ -59,6 +59,7 @@ struct core_info {
  43         cpumask_t mask;
  44  };
  45
  46 +static int topology_enabled;
  47  static void topology_work_fn(struct work_struct *work);
  48  static struct tl_info *tl_info;
  49  static struct core_info core_info;
  50 @@ -79,7 +80,7 @@ cpumask_t cpu_coregroup_map(unsigned int
  51         cpumask_t mask;
  52
  53         cpus_clear(mask);
  54 -       if (!machine_has_topology)
  55 +       if (!topology_enabled || !machine_has_topology)
  56                 return cpu_present_map;
  57         spin_lock_irqsave(&topology_lock, flags);
  58         while (core) {
  59 @@ -264,6 +265,15 @@ static void topology_interrupt(__u16 cod
  60         schedule_work(&topology_work);
  61  }
  62
  63 +static int __init early_parse_topology(char *p)
  64 +{
  65 +       if (strncmp(p, "on", 2))
  66 +               return 0;
  67 +       topology_enabled = 1;
  68 +       return 0;
  69 +}
  70 +early_param("topology", early_parse_topology);
  71 +
  72  static int __init init_topology_update(void)
  73  {
  74         int rc;