src/patches/suse-2.6.27.39/patches.fixes/cpufreq_ondemand_performance_optimise_default_settings.patch

   1 From: Thomas Renninger <trenn@suse.de>
   2 Subject: CPUFREQ: ondemand: Limit default sampling rate to 300ms max.
   3 References: bnc#464461
   4 Patch-Mainline: never, SLE11 only
   5
   6 HW cpufreq drivers (e.g. all non-acpi AMD) may report too high latency values.
   7 The default sampling rate (how often the ondemand/conservative governor
   8 checks for frequency adjustments) may therefore be much too high,
   9 resulting in performance loss.
  10
  11 Restrict default sampling rate to 300ms. 333ms sampling rate is field
  12 tested with userspace governors, 300ms should be a fine maximum default
  13 value for the ondemand kernel governor for all HW out there.
  14
  15 Set default up_threshold to 40 on multi core systems.
  16 This should avoid effects where two CPU intensive threads are waiting on
  17 each other on separate cores. On a single core machine these would all be
  18 processed on one core resulting in higher utilization of the one core.
  19
  20 ---
  21  drivers/cpufreq/cpufreq_ondemand.c |   26 ++++++++++++++++++++++++++
  22  1 file changed, 26 insertions(+)
  23
  24 Index: linux-2.6.27/drivers/cpufreq/cpufreq_ondemand.c
  25 ===================================================================
  26 --- linux-2.6.27.orig/drivers/cpufreq/cpufreq_ondemand.c
  27 +++ linux-2.6.27/drivers/cpufreq/cpufreq_ondemand.c
  28 @@ -58,6 +58,7 @@ static unsigned int def_sampling_rate;
  29  #define MAX_SAMPLING_RATE                      (500 * def_sampling_rate)
  30  #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER   (1000)
  31  #define TRANSITION_LATENCY_LIMIT               (10 * 1000 * 1000)
  32 +#define MAX_DEFAULT_SAMPLING_RATE              (300 * 1000)
  33
  34  static void do_dbs_timer(struct work_struct *work);
  35
  36 @@ -558,6 +559,31 @@ static int cpufreq_governor_dbs(struct c
  37                         if (def_sampling_rate < MIN_STAT_SAMPLING_RATE)
  38                                 def_sampling_rate = MIN_STAT_SAMPLING_RATE;
  39
  40 +                       /*
  41 +                        * Cut def_sampling rate to 300ms if it was above,
  42 +                        * still consider to not set it above latency
  43 +                        * transition * 100
  44 +                        */
  45 +                       if (def_sampling_rate > MAX_DEFAULT_SAMPLING_RATE) {
  46 +                               def_sampling_rate =
  47 +                                       (MAX_DEFAULT_SAMPLING_RATE < MINIMUM_SAMPLING_RATE)
  48 +                                       ? MINIMUM_SAMPLING_RATE : MAX_DEFAULT_SAMPLING_RATE;
  49 +                               printk(KERN_INFO "CPUFREQ: ondemand sampling "
  50 +                                      "rate set to %d ms\n",
  51 +                                      def_sampling_rate / 1000);
  52 +                       }
  53 +                       /*
  54 +                        * Be conservative in respect to performance.
  55 +                        * If an application calculates using two threads
  56 +                        * depending on each other, they will be run on several
  57 +                        * CPU cores resulting on 50% load on both.
  58 +                        * SLED might still want to prefer 80% up_threshold
  59 +                        * by default, but we cannot differ that here.
  60 +                        */
  61 +                       if (num_online_cpus() > 1)
  62 +                               dbs_tuners_ins.up_threshold =
  63 +                                       DEF_FREQUENCY_UP_THRESHOLD / 2;
  64 +
  65                         dbs_tuners_ins.sampling_rate = def_sampling_rate;
  66                 }
  67                 dbs_timer_init(this_dbs_info);