calc_load() is called by timer interrupt to update avenrun[]. It currently calls nr_active() at each timer tick (HZ per second), while the update of avenrun[] is done only once every 5 seconds. (LOAD_FREQ=5 Hz) nr_active() is quite expensive on SMP machines, since it has to sum up nr_running and nr_uninterruptible of all online CPUS, bringing foreign dirty cache lines. This patch is an optimization of calc_load() so that nr_active() is called only if we need it. The use of unlikely() is welcome since the condition is true only once every 5*HZ time.
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| @@ -1146,11 +1146,15 @@ static inline void calc_load(unsigned long ticks) · 1145 unmodified lines | |||
| 1146 | unsigned long active_tasks; /* fixed-point */ | 1146 | unsigned long active_tasks; /* fixed-point */ |
| 1147 | static int count = LOAD_FREQ; | 1147 | static int count = LOAD_FREQ; |
| 1148 | 1148 | ||
| 1149 | active_tasks = count_active_tasks(); | 1149 | count -= ticks; |
| 1150 | for (count -= ticks; count < 0; count += LOAD_FREQ) { | 1150 | if (unlikely(count < 0)) { |
| 1151 | CALC_LOAD(avenrun[0], EXP_1, active_tasks); | 1151 | active_tasks = count_active_tasks(); |
| 1152 | CALC_LOAD(avenrun[1], EXP_5, active_tasks); | 1152 | do { |
| 1153 | CALC_LOAD(avenrun[2], EXP_15, active_tasks); | 1153 | CALC_LOAD(avenrun[0], EXP_1, active_tasks); |
| 1154 | CALC_LOAD(avenrun[1], EXP_5, active_tasks); | ||
| 1155 | CALC_LOAD(avenrun[2], EXP_15, active_tasks); | ||
| 1156 | count += LOAD_FREQ; | ||
| 1157 | } while (count < 0); | ||
| 1154 | } | 1158 | } |
| 1155 | } | 1159 | } |
| 1156 | 1160 | ||