Re: [PATCH 2/2] tracing/workqueue: separate singlethreadedworkqueues

From: Frederic Weisbecker
Date: Sun Jan 25 2009 - 10:56:58 EST

On Thu, Jan 22, 2009 at 05:05:34PM -0800, Frederic Weisbecker wrote:
> When a singlethread thread is added on the list, it is
> appended to the first cpu workqueues. This is a mistake because
> singlethreaded workqueues are not bounded to specific cpu but
> on all online cpus.
>
> On their cpu column, we will now find a * character.
>
> # CPU INSERTED EXECUTED NAME
> # | | | |
>
> * 0 0 kpsmoused
> * 0 0 ata_aux
> * 0 0 cqueue
> * 0 0 kacpi_notify
> * 0 0 kacpid
> * 998 998 khelper
> * 0 0 cpuset
>
> 1 0 0 hda0/1
> 1 42 42 reiserfs/1
> 1 0 0 scsi_tgtd/1
> 1 0 0 aio/1
> 1 0 0 ata/1
> 1 193 193 kblockd/1
> 1 0 0 kintegrityd/1
> 1 4 4 work_on_cpu/1
> 1 1244 1244 events/1
>
> 0 0 0 hda0/0
> 0 63 63 reiserfs/0
> 0 0 0 scsi_tgtd/0
> 0 0 0 aio/0
> 0 0 0 ata/0
> 0 188 188 kblockd/0
> 0 0 0 kintegrityd/0
> 0 16 16 work_on_cpu/0
> 0 1360 1360 events/0
>
> Hmm, it looks like most of these workqueues are pointless :-)
>
> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> ---
> include/trace/workqueue.h | 16 +++--
> kernel/trace/trace_workqueue.c | 143 +++++++++++++++++++++++++++-------------
> kernel/workqueue.c | 11 ++-
> 3 files changed, 115 insertions(+), 55 deletions(-)
>
> diff --git a/include/trace/workqueue.h b/include/trace/workqueue.h
> index 867829d..4769c2d 100644
> --- a/include/trace/workqueue.h
> +++ b/include/trace/workqueue.h
> @@ -5,13 +5,17 @@
> #include <linux/workqueue.h>
> #include <linux/sched.h>
>
> +#define SINGLETHREAD_CPU -1
> +
> DECLARE_TRACE(workqueue_insertion,
> - TPPROTO(struct task_struct *wq_thread, struct work_struct *work),
> - TPARGS(wq_thread, work));
> + TPPROTO(struct task_struct *wq_thread, struct work_struct *work,
> + int singlethread),
> + TPARGS(wq_thread, work, singlethread));
>
> DECLARE_TRACE(workqueue_execution,
> - TPPROTO(struct task_struct *wq_thread, struct work_struct *work),
> - TPARGS(wq_thread, work));
> + TPPROTO(struct task_struct *wq_thread, struct work_struct *work,
> + int singlethread),
> + TPARGS(wq_thread, work, singlethread));
>
> /* Trace the creation of one workqueue thread on a cpu */
> DECLARE_TRACE(workqueue_creation,
> @@ -19,7 +23,7 @@ DECLARE_TRACE(workqueue_creation,
> TPARGS(wq_thread, cpu));
>
> DECLARE_TRACE(workqueue_destruction,
> - TPPROTO(struct task_struct *wq_thread),
> - TPARGS(wq_thread));
> + TPPROTO(struct task_struct *wq_thread, int singlethread),
> + TPARGS(wq_thread, singlethread));
>
> #endif /* __TRACE_WORKQUEUE_H */
> diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
> index 4664990..38a1291 100644
> --- a/kernel/trace/trace_workqueue.c
> +++ b/kernel/trace/trace_workqueue.c
> @@ -12,7 +12,6 @@
> #include "trace_stat.h"
> #include "trace.h"
>
> -
> /* A cpu workqueue thread */
> struct cpu_workqueue_stats {
> struct list_head list;
> @@ -41,18 +40,28 @@ struct workqueue_global_stats {
> static DEFINE_PER_CPU(struct workqueue_global_stats, all_workqueue_stat);
> #define workqueue_cpu_stat(cpu) (&per_cpu(all_workqueue_stat, cpu))
>
> +static struct workqueue_global_stats singlethread_stat;
> +
> +
> /* Insertion of a work */
> static void
> probe_workqueue_insertion(struct task_struct *wq_thread,
> - struct work_struct *work)
> + struct work_struct *work, int singlethread)
> {
> - int cpu = cpumask_first(&wq_thread->cpus_allowed);
> + struct workqueue_global_stats *stats;
> struct cpu_workqueue_stats *node, *next;
> unsigned long flags;
> + int cpu;
> +
> + if (singlethread)
> + stats = &singlethread_stat;
> + else {
> + cpu = cpumask_first(&wq_thread->cpus_allowed);
> + stats = workqueue_cpu_stat(cpu);
> + }
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> - list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
> - list) {
> + spin_lock_irqsave(&stats->lock, flags);
> + list_for_each_entry_safe(node, next, &stats->list, list) {
> if (node->pid == wq_thread->pid) {
> atomic_inc(&node->inserted);
> goto found;
> @@ -60,21 +69,28 @@ probe_workqueue_insertion(struct task_struct *wq_thread,
> }
> pr_debug("trace_workqueue: entry not found\n");
> found:
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + spin_unlock_irqrestore(&stats->lock, flags);
> }
>
> /* Execution of a work */
> static void
> probe_workqueue_execution(struct task_struct *wq_thread,
> - struct work_struct *work)
> + struct work_struct *work, int singlethread)
> {
> - int cpu = cpumask_first(&wq_thread->cpus_allowed);
> struct cpu_workqueue_stats *node, *next;
> + struct workqueue_global_stats *stats;
> unsigned long flags;
> + int cpu;
> +
> + if (singlethread)
> + stats = &singlethread_stat;
> + else {
> + cpu = cpumask_first(&wq_thread->cpus_allowed);
> + stats = workqueue_cpu_stat(cpu);
> + }
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> - list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
> - list) {
> + spin_lock_irqsave(&stats->lock, flags);
> + list_for_each_entry_safe(node, next, &stats->list, list) {
> if (node->pid == wq_thread->pid) {
> node->executed++;
> goto found;
> @@ -82,17 +98,16 @@ probe_workqueue_execution(struct task_struct *wq_thread,
> }
> pr_debug("trace_workqueue: entry not found\n");
> found:
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + spin_unlock_irqrestore(&stats->lock, flags);
> }
>
> /* Creation of a cpu workqueue thread */
> static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
> {
> + struct workqueue_global_stats *stats;
> struct cpu_workqueue_stats *cws;
> unsigned long flags;
>
> - WARN_ON(cpu < 0 || cpu >= num_possible_cpus());
> -
> /* Workqueues are sometimes created in atomic context */
> cws = kzalloc(sizeof(struct cpu_workqueue_stats), GFP_ATOMIC);
> if (!cws) {
> @@ -103,27 +118,39 @@ static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
>
> INIT_LIST_HEAD(&cws->list);
> cws->cpu = cpu;
> -
> cws->pid = wq_thread->pid;
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> - if (list_empty(&workqueue_cpu_stat(cpu)->list))
> + if (cpu == SINGLETHREAD_CPU)
> + stats = &singlethread_stat;
> + else
> + stats = workqueue_cpu_stat(cpu);
> +
> +
> + spin_lock_irqsave(&stats->lock, flags);
> + if (list_empty(&stats->list))
> cws->first_entry = true;
> - list_add_tail(&cws->list, &workqueue_cpu_stat(cpu)->list);
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + list_add_tail(&cws->list, &stats->list);
> + spin_unlock_irqrestore(&stats->lock, flags);
> }
>
> /* Destruction of a cpu workqueue thread */
> -static void probe_workqueue_destruction(struct task_struct *wq_thread)
> +static void probe_workqueue_destruction(struct task_struct *wq_thread,
> + int singlethread)
> {
> - /* Workqueue only execute on one cpu */
> - int cpu = cpumask_first(&wq_thread->cpus_allowed);
> struct cpu_workqueue_stats *node, *next;
> + struct workqueue_global_stats *stats;
> unsigned long flags;
> + int cpu;
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> - list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
> - list) {
> + if (singlethread)
> + stats = &singlethread_stat;
> + else {
> + cpu = cpumask_first(&wq_thread->cpus_allowed);
> + stats = workqueue_cpu_stat(cpu);
> + }
> +
> + spin_lock_irqsave(&stats->lock, flags);
> + list_for_each_entry_safe(node, next, &stats->list, list) {
> if (node->pid == wq_thread->pid) {
> list_del(&node->list);
> kfree(node);
> @@ -133,23 +160,28 @@ static void probe_workqueue_destruction(struct task_struct *wq_thread)
>
> pr_debug("trace_workqueue: don't find workqueue to destroy\n");
> found:
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + spin_unlock_irqrestore(&stats->lock, flags);
>
> }
>
> static struct cpu_workqueue_stats *workqueue_stat_start_cpu(int cpu)
> {
> unsigned long flags;
> + struct workqueue_global_stats *stats;
> struct cpu_workqueue_stats *ret = NULL;
>
> + if (cpu == SINGLETHREAD_CPU)
> + stats = &singlethread_stat;
> + else
> + stats = workqueue_cpu_stat(cpu);
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> + spin_lock_irqsave(&stats->lock, flags);
>
> - if (!list_empty(&workqueue_cpu_stat(cpu)->list))
> - ret = list_entry(workqueue_cpu_stat(cpu)->list.next,
> + if (!list_empty(&stats->list))
> + ret = list_entry(stats->list.next,
> struct cpu_workqueue_stats, list);
>
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + spin_unlock_irqrestore(&stats->lock, flags);
>
> return ret;
> }
> @@ -170,41 +202,59 @@ static void *workqueue_stat_start(void)
> static void *workqueue_stat_next(void *prev, int idx)
> {
> struct cpu_workqueue_stats *prev_cws = prev;
> + struct workqueue_global_stats *stats;
> int cpu = prev_cws->cpu;
> unsigned long flags;
> void *ret = NULL;
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> - if (list_is_last(&prev_cws->list, &workqueue_cpu_stat(cpu)->list)) {
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + if (cpu == SINGLETHREAD_CPU)
> + stats = &singlethread_stat;
> + else
> + stats = workqueue_cpu_stat(cpu);
> +
> + spin_lock_irqsave(&stats->lock, flags);
> + if (list_is_last(&prev_cws->list, &stats->list)) {
> + spin_unlock_irqrestore(&stats->lock, flags);
> + if (cpu == SINGLETHREAD_CPU)
> + return NULL;
> for (++cpu ; cpu < num_possible_cpus(); cpu++) {
> ret = workqueue_stat_start_cpu(cpu);
> if (ret)
> return ret;
> }
> - return NULL;
> + /* Display singlethreaded at last */
> + return workqueue_stat_start_cpu(SINGLETHREAD_CPU);
> }
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + ret = list_entry(prev_cws->list.next, struct cpu_workqueue_stats, list);
> + spin_unlock_irqrestore(&stats->lock, flags);
>
> - return list_entry(prev_cws->list.next, struct cpu_workqueue_stats,
> - list);
> + return ret;
> }
>
> static int workqueue_stat_show(struct seq_file *s, void *p)
> {
> struct cpu_workqueue_stats *cws = p;
> + struct workqueue_global_stats *stats;
> unsigned long flags;
> int cpu = cws->cpu;
>
> - seq_printf(s, "%3d %6d %6u %s\n", cws->cpu,
> - atomic_read(&cws->inserted),
> - cws->executed,
> - trace_find_cmdline(cws->pid));
> + if (cpu == SINGLETHREAD_CPU) {
> + stats = &singlethread_stat;
> + seq_printf(s, " * ");
> + } else {
> + stats = workqueue_cpu_stat(cpu);
> + seq_printf(s, "%3d ", cpu);
> + }
> +
>
> - spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> - if (&cws->list == workqueue_cpu_stat(cpu)->list.next)
> + seq_printf(s, "%6d %6u %s\n", atomic_read(&cws->inserted),
> + cws->executed,
> + trace_find_cmdline(cws->pid));
> +
> + spin_lock_irqsave(&stats->lock, flags);
> + if (&cws->list == stats->list.next)
> seq_printf(s, "\n");
> - spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
> + spin_unlock_irqrestore(&stats->lock, flags);
>
> return 0;
> }
> @@ -265,6 +315,9 @@ int __init trace_workqueue_early_init(void)
> INIT_LIST_HEAD(&workqueue_cpu_stat(cpu)->list);
> }
>
> + spin_lock_init(&singlethread_stat.lock);
> + INIT_LIST_HEAD(&singlethread_stat.list);
> +
> return 0;
>
> no_creation:
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index e53ee18..936b037 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -131,7 +131,7 @@ DEFINE_TRACE(workqueue_insertion);
> static void insert_work(struct cpu_workqueue_struct *cwq,
> struct work_struct *work, struct list_head *head)
> {
> - trace_workqueue_insertion(cwq->thread, work);
> + trace_workqueue_insertion(cwq->thread, work, cwq->wq->singlethread);
>
> set_wq_data(work, cwq);
> /*
> @@ -291,7 +291,9 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
> */
> struct lockdep_map lockdep_map = work->lockdep_map;
> #endif
> - trace_workqueue_execution(cwq->thread, work);
> + struct workqueue_struct *wq = cwq->wq;
> +
> + trace_workqueue_execution(cwq->thread, work, wq->singlethread);
> cwq->current_work = work;
> list_del_init(cwq->worklist.next);
> spin_unlock_irq(&cwq->lock);
> @@ -796,7 +798,8 @@ static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
> sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
> cwq->thread = p;
>
> - trace_workqueue_creation(cwq->thread, cpu);
> + trace_workqueue_creation(cwq->thread, wq->singlethread ?
> + SINGLETHREAD_CPU : cpu);
>
> return 0;
> }
> @@ -904,7 +907,7 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
> * checks list_empty(), and a "normal" queue_work() can't use
> * a dead CPU.
> */
> - trace_workqueue_destruction(cwq->thread);
> + trace_workqueue_destruction(cwq->thread, cwq->wq->singlethread);
> kthread_stop(cwq->thread);
> cwq->thread = NULL;
> }
> --
> 1.6.0.4
>
>


Cc'ed Lai!

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