最近在看进程调度部分，ULK3和源码感觉有点对不上，请各位指点

dengcainiao

贴一段ULK3的描述，摘自7.4.3描述recalc_task_prio( ) 功能的第三点

Checks whether the process is not a kernel thread, whether it is awakening from the TASK_UNINTERRUPTIBLE state (p->activated field equal to -1; see step 5 in the previous section), and whether it has been continuously asleep beyond a given sleep time threshold. If these three conditions are fulfilled, the function sets the p->sleep_avg field to the equivalent of 900 ticks (an empirical value obtained by subtracting the duration of the base time quantum of a standard process from the maximum average sleep time). Then, it jumps to step 8.

The sleep time threshold depends on the static priority of the process; some typical values are shown in Table 7-2. In short, the goal of this empirical rule is to ensure that processes that have been asleep for a long time in uninterruptible modeusually waiting for disk I/O operations get a predefined sleep average value that is large enough to allow them to be quickly serviced, but it is also not so large to cause starvation for other processes.


现在给大家贴上源码，摘自2.6.11.1内核
static void recalc_task_prio(task_t *p, unsigned long long now)
{
        unsigned long long __sleep_time = now - p->timestamp;
        unsigned long sleep_time;

        if (__sleep_time > NS_MAX_SLEEP_AVG)
                sleep_time = NS_MAX_SLEEP_AVG;
        else
                sleep_time = (unsigned long)__sleep_time;

        if (likely(sleep_time > 0)) {
                /*
                 * User tasks that sleep a long time are categorised as
                 * idle and will get just interactive status to stay active &
                 * prevent them suddenly becoming cpu hogs and starving
                 * other processes.
                 */
                if (p->mm && p->activated != -1 &&//注意这里，和ULK3上说的一致吗？？？
                        sleep_time > INTERACTIVE_SLEEP(p)) {
                                p->sleep_avg = JIFFIES_TO_NS(MAX_SLEEP_AVG -
                                                DEF_TIMESLICE);
                } else {
                        /*
                         * The lower the sleep avg a task has the more
                         * rapidly it will rise with sleep time.
                         */
                        sleep_time *= (MAX_BONUS - CURRENT_BONUS(p)) ? : 1;

                        /*
                         * Tasks waking from uninterruptible sleep are
                         * limited in their sleep_avg rise as they
                         * are likely to be waiting on I/O
                         */
                        if (p->activated == -1 && p->mm) {
                                if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
                                        sleep_time = 0;
                                else if (p->sleep_avg + sleep_time >=
                                                INTERACTIVE_SLEEP(p)) {
                                        p->sleep_avg = INTERACTIVE_SLEEP(p);
                                        sleep_time = 0;
                                }
                        }

                        /*
                         * This code gives a bonus to interactive tasks.
                         *
                         * The boost works by updating the 'average sleep time'
                         * value here, based on ->timestamp. The more time a
                         * task spends sleeping, the higher the average gets -
                         * and the higher the priority boost gets as well.
                         */
                        p->sleep_avg += sleep_time;

                        if (p->sleep_avg > NS_MAX_SLEEP_AVG)
                                p->sleep_avg = NS_MAX_SLEEP_AVG;
                }
        }

        p->prio = effective_prio(p);
}

dengcainiao

我感觉if (p->mm && p->activated == -1 &&//这里应该是==-1才和ULK3上说的一致吗。。
                        sleep_time > INTERACTIVE_SLEEP(p)) {
                                p->sleep_avg = JIFFIES_TO_NS(MAX_SLEEP_AVG -
                                                DEF_TIMESLICE);
                }