[PATCH 2/2] tracing/workqueue: separate singlethreaded workqueues

From: Frederic Weisbecker
Date: Thu Jan 22 2009 - 20:05:48 EST

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


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