![Bharath Ravi](/assets/img/avatar_default.png)
This patch corrects the incorrect value of per process run-queue wait time reported by delay statistics. The anomaly was due to the following reason. When a process leaves the CPU and immediately starts waiting for CPU on the runqueue (which means it remains in the TASK_RUNNABLE state), the time of re-entry into the run-queue is never recorded. Due to this, the waiting time on the runqueue from this point of re-entry upto the next time it hits the CPU is not accounted for. This is solved by recording the time of re-entry of a process leaving the CPU in the sched_info_depart() function IF the process will go back to waiting on the run-queue. This IF condition is verified by checking whether the process is still in the TASK_RUNNABLE state. The patch was tested on 2.6.26-rc6 using two simple CPU hog programs. The values noted prior to the fix did not account for the time spent on the runqueue waiting. After the fix, the correct values were reported back to user space. Signed-off-by: Bharath Ravi <bharathravi1@gmail.com> Signed-off-by: Madhava K R <madhavakr@gmail.com> Cc: dhaval@linux.vnet.ibm.com Cc: vatsa@in.ibm.com Cc: balbir@in.ibm.com Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
249 lines
7.4 KiB
C
249 lines
7.4 KiB
C
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#ifdef CONFIG_SCHEDSTATS
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/*
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* bump this up when changing the output format or the meaning of an existing
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* format, so that tools can adapt (or abort)
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*/
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#define SCHEDSTAT_VERSION 14
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static int show_schedstat(struct seq_file *seq, void *v)
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{
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int cpu;
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int mask_len = NR_CPUS/32 * 9;
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char *mask_str = kmalloc(mask_len, GFP_KERNEL);
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if (mask_str == NULL)
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return -ENOMEM;
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seq_printf(seq, "version %d\n", SCHEDSTAT_VERSION);
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seq_printf(seq, "timestamp %lu\n", jiffies);
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for_each_online_cpu(cpu) {
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struct rq *rq = cpu_rq(cpu);
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#ifdef CONFIG_SMP
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struct sched_domain *sd;
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int dcount = 0;
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#endif
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/* runqueue-specific stats */
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seq_printf(seq,
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"cpu%d %u %u %u %u %u %u %u %u %u %llu %llu %lu",
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cpu, rq->yld_both_empty,
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rq->yld_act_empty, rq->yld_exp_empty, rq->yld_count,
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rq->sched_switch, rq->sched_count, rq->sched_goidle,
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rq->ttwu_count, rq->ttwu_local,
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rq->rq_sched_info.cpu_time,
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rq->rq_sched_info.run_delay, rq->rq_sched_info.pcount);
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seq_printf(seq, "\n");
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#ifdef CONFIG_SMP
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/* domain-specific stats */
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preempt_disable();
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for_each_domain(cpu, sd) {
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enum cpu_idle_type itype;
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cpumask_scnprintf(mask_str, mask_len, sd->span);
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seq_printf(seq, "domain%d %s", dcount++, mask_str);
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for (itype = CPU_IDLE; itype < CPU_MAX_IDLE_TYPES;
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itype++) {
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seq_printf(seq, " %u %u %u %u %u %u %u %u",
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sd->lb_count[itype],
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sd->lb_balanced[itype],
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sd->lb_failed[itype],
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sd->lb_imbalance[itype],
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sd->lb_gained[itype],
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sd->lb_hot_gained[itype],
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sd->lb_nobusyq[itype],
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sd->lb_nobusyg[itype]);
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}
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seq_printf(seq,
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" %u %u %u %u %u %u %u %u %u %u %u %u\n",
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sd->alb_count, sd->alb_failed, sd->alb_pushed,
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sd->sbe_count, sd->sbe_balanced, sd->sbe_pushed,
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sd->sbf_count, sd->sbf_balanced, sd->sbf_pushed,
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sd->ttwu_wake_remote, sd->ttwu_move_affine,
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sd->ttwu_move_balance);
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}
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preempt_enable();
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#endif
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}
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kfree(mask_str);
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return 0;
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}
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static int schedstat_open(struct inode *inode, struct file *file)
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{
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unsigned int size = PAGE_SIZE * (1 + num_online_cpus() / 32);
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char *buf = kmalloc(size, GFP_KERNEL);
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struct seq_file *m;
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int res;
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if (!buf)
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return -ENOMEM;
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res = single_open(file, show_schedstat, NULL);
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if (!res) {
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m = file->private_data;
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m->buf = buf;
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m->size = size;
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} else
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kfree(buf);
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return res;
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}
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const struct file_operations proc_schedstat_operations = {
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.open = schedstat_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = single_release,
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};
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/*
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* Expects runqueue lock to be held for atomicity of update
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*/
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static inline void
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rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
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{
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if (rq) {
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rq->rq_sched_info.run_delay += delta;
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rq->rq_sched_info.pcount++;
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}
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}
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/*
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* Expects runqueue lock to be held for atomicity of update
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*/
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static inline void
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rq_sched_info_depart(struct rq *rq, unsigned long long delta)
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{
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if (rq)
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rq->rq_sched_info.cpu_time += delta;
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}
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# define schedstat_inc(rq, field) do { (rq)->field++; } while (0)
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# define schedstat_add(rq, field, amt) do { (rq)->field += (amt); } while (0)
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# define schedstat_set(var, val) do { var = (val); } while (0)
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#else /* !CONFIG_SCHEDSTATS */
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static inline void
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rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
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{}
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static inline void
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rq_sched_info_depart(struct rq *rq, unsigned long long delta)
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{}
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# define schedstat_inc(rq, field) do { } while (0)
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# define schedstat_add(rq, field, amt) do { } while (0)
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# define schedstat_set(var, val) do { } while (0)
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#endif
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#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
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/*
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* Called when a process is dequeued from the active array and given
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* the cpu. We should note that with the exception of interactive
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* tasks, the expired queue will become the active queue after the active
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* queue is empty, without explicitly dequeuing and requeuing tasks in the
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* expired queue. (Interactive tasks may be requeued directly to the
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* active queue, thus delaying tasks in the expired queue from running;
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* see scheduler_tick()).
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*
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* This function is only called from sched_info_arrive(), rather than
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* dequeue_task(). Even though a task may be queued and dequeued multiple
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* times as it is shuffled about, we're really interested in knowing how
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* long it was from the *first* time it was queued to the time that it
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* finally hit a cpu.
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*/
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static inline void sched_info_dequeued(struct task_struct *t)
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{
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t->sched_info.last_queued = 0;
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}
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/*
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* Called when a task finally hits the cpu. We can now calculate how
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* long it was waiting to run. We also note when it began so that we
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* can keep stats on how long its timeslice is.
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*/
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static void sched_info_arrive(struct task_struct *t)
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{
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unsigned long long now = task_rq(t)->clock, delta = 0;
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if (t->sched_info.last_queued)
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delta = now - t->sched_info.last_queued;
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sched_info_dequeued(t);
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t->sched_info.run_delay += delta;
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t->sched_info.last_arrival = now;
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t->sched_info.pcount++;
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rq_sched_info_arrive(task_rq(t), delta);
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}
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/*
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* Called when a process is queued into either the active or expired
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* array. The time is noted and later used to determine how long we
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* had to wait for us to reach the cpu. Since the expired queue will
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* become the active queue after active queue is empty, without dequeuing
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* and requeuing any tasks, we are interested in queuing to either. It
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* is unusual but not impossible for tasks to be dequeued and immediately
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* requeued in the same or another array: this can happen in sched_yield(),
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* set_user_nice(), and even load_balance() as it moves tasks from runqueue
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* to runqueue.
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*
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* This function is only called from enqueue_task(), but also only updates
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* the timestamp if it is already not set. It's assumed that
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* sched_info_dequeued() will clear that stamp when appropriate.
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*/
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static inline void sched_info_queued(struct task_struct *t)
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{
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if (unlikely(sched_info_on()))
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if (!t->sched_info.last_queued)
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t->sched_info.last_queued = task_rq(t)->clock;
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}
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/*
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* Called when a process ceases being the active-running process, either
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* voluntarily or involuntarily. Now we can calculate how long we ran.
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* Also, if the process is still in the TASK_RUNNING state, call
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* sched_info_queued() to mark that it has now again started waiting on
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* the runqueue.
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*/
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static inline void sched_info_depart(struct task_struct *t)
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{
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unsigned long long delta = task_rq(t)->clock -
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t->sched_info.last_arrival;
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t->sched_info.cpu_time += delta;
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rq_sched_info_depart(task_rq(t), delta);
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if (t->state == TASK_RUNNING)
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sched_info_queued(t);
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}
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/*
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* Called when tasks are switched involuntarily due, typically, to expiring
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* their time slice. (This may also be called when switching to or from
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* the idle task.) We are only called when prev != next.
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*/
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static inline void
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__sched_info_switch(struct task_struct *prev, struct task_struct *next)
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{
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struct rq *rq = task_rq(prev);
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/*
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* prev now departs the cpu. It's not interesting to record
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* stats about how efficient we were at scheduling the idle
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* process, however.
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*/
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if (prev != rq->idle)
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sched_info_depart(prev);
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if (next != rq->idle)
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sched_info_arrive(next);
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}
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static inline void
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sched_info_switch(struct task_struct *prev, struct task_struct *next)
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{
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if (unlikely(sched_info_on()))
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__sched_info_switch(prev, next);
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}
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#else
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#define sched_info_queued(t) do { } while (0)
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#define sched_info_switch(t, next) do { } while (0)
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#endif /* CONFIG_SCHEDSTATS || CONFIG_TASK_DELAY_ACCT */
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