Message-ID: <alpine.DEB.1.10.0901121314190.22796@gandalf.stny.rr.com>
Date:	Mon, 12 Jan 2009 13:15:49 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 2/2] [RESEND] tracing: Add a new workqueue tracer




On Sat, 10 Jan 2009, Frederic Weisbecker wrote:

> Sorry I lost two files in the previous 2/2 patch.
> Here is the true version
> --
> 
> The workqueue tracer provides some statistical informations
> about each cpu workqueue thread such as the number of the
> works inserted and executed since their creation. It can help
> to evaluate the amount of work each of them have to perform.
> For example it can help a developer to decide whether he should
> choose a per cpu workqueue instead of a singlethreaded one.
> 
> It only traces statistical informations for now but it will probably later
> provide event tracing too.
> 
> Such a tracer could help too, and be improved, to help rt priority sorted
> workqueue development.
> 
> To have a snapshot of the workqueues state at any time, just do
> 
> cat /debugfs/tracing/trace_stat/workqueues
> 
> Ie:
> 
> # CPU  INSERTED  EXECUTED   NAME
> # |      |         |          |
> 
>   1    125        125       reiserfs/1
>   1      0          0       scsi_tgtd/1
>   1      0          0       aio/1
>   1      0          0       ata/1
>   1    114        114       kblockd/1
>   1      0          0       kintegrityd/1
>   1   2144       2147       events/1
> 
>   0      0          0       kpsmoused
>   0    105        105       reiserfs/0
>   0      0          0       scsi_tgtd/0
>   0      0          0       aio/0
>   0      0          0       ata_aux
>   0      0          0       ata/0
>   0      0          0       cqueue
>   0      0          0       kacpi_notify
>   0      0          0       kacpid
>   0    149        149       kblockd/0
>   0      0          0       kintegrityd/0
>   0   1000       1000       khelper
>   0   2258       2270       events/0
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  include/trace/workqueue.h      |   25 ++++
>  kernel/trace/Kconfig           |   11 ++
>  kernel/trace/Makefile          |    1 +
>  kernel/trace/trace_workqueue.c |  273 ++++++++++++++++++++++++++++++++++++++++
>  kernel/workqueue.c             |   16 +++-
>  5 files changed, 325 insertions(+), 1 deletions(-)
> 
> diff --git a/include/trace/workqueue.h b/include/trace/workqueue.h
> new file mode 100644
> index 0000000..867829d
> --- /dev/null
> +++ b/include/trace/workqueue.h
> @@ -0,0 +1,25 @@
> +#ifndef __TRACE_WORKQUEUE_H
> +#define __TRACE_WORKQUEUE_H
> +
> +#include <linux/tracepoint.h>
> +#include <linux/workqueue.h>
> +#include <linux/sched.h>
> +
> +DECLARE_TRACE(workqueue_insertion,
> +	   TPPROTO(struct task_struct *wq_thread, struct work_struct *work),
> +	   TPARGS(wq_thread, work));
> +
> +DECLARE_TRACE(workqueue_execution,
> +	   TPPROTO(struct task_struct *wq_thread, struct work_struct *work),
> +	   TPARGS(wq_thread, work));
> +
> +/* Trace the creation of one workqueue thread on a cpu */
> +DECLARE_TRACE(workqueue_creation,
> +	   TPPROTO(struct task_struct *wq_thread, int cpu),
> +	   TPARGS(wq_thread, cpu));
> +
> +DECLARE_TRACE(workqueue_destruction,
> +	   TPPROTO(struct task_struct *wq_thread),
> +	   TPARGS(wq_thread));
> +
> +#endif /* __TRACE_WORKQUEUE_H */
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 1c0b750..9ba1c68 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -284,6 +284,17 @@ config KMEMTRACE
>  
>  	  If unsure, say N.
>  
> +config WORKQUEUE_TRACER
> +	bool "Trace workqueues"
> +	select TRACING
> +	help
> +	  The workqueue tracer provides some statistical informations
> +          about each cpu workqueue thread such as the number of the
> +          works inserted and executed since their creation. It can help
> +          to evaluate the amount of work each of them have to perform.
> +          For example it can help a developer to decide whether he should
> +          choose a per cpu workqueue instead of a singlethreaded one.
> + 
>  
>  config DYNAMIC_FTRACE
>  	bool "enable/disable ftrace tracepoints dynamically"
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index 05c9182..f76d48f 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -36,5 +36,6 @@ obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
>  obj-$(CONFIG_HW_BRANCH_TRACER) += trace_hw_branches.o
>  obj-$(CONFIG_POWER_TRACER) += trace_power.o
>  obj-$(CONFIG_KMEMTRACE) += kmemtrace.o
> +obj-$(CONFIG_WORKQUEUE_TRACER) += trace_workqueue.o
>  
>  libftrace-y := ftrace.o
> diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
> new file mode 100644
> index 0000000..f006135
> --- /dev/null
> +++ b/kernel/trace/trace_workqueue.c
> @@ -0,0 +1,273 @@
> +/*
> + * Workqueue statistical tracer.
> + *
> + * Copyright (C) 2008 Frederic Weisbecker <fweisbec@...il.com>
> + *
> + */
> +
> +
> +#include <trace/workqueue.h>
> +#include <linux/list.h>
> +#include "trace_stat.h"
> +#include "trace.h"
> +
> +
> +/* A list of cpu workqueue threads on one Cpu */
> +struct cpu_workqueue_stats {
> +	struct list_head            list;
> +/* Useful to know if we print the cpu headers */
> +	bool		            first_entry;
> +	int		            cpu;
> +	pid_t 			    pid;
> +/* Can be inserted from interrupt or user context, need to be atomic */
> +	atomic_t 	            inserted;
> +/*
> + *  Don't need to be atomic, works are serialized in a single workqueue thread
> + *  on a single CPU.
> + */
> +	unsigned int 	 	    executed;
> +};
> +
> +
> +
> +static spinlock_t	cpu_wq_list_lock[NR_CPUS];
> +
> +/* List of cpu workqueue thread, listed by cpu */
> +static struct list_head cpu_wq_list[NR_CPUS];
> +
> +/* Insertion of a work */
> +static void
> +probe_workqueue_insertion(struct task_struct *wq_thread,
> +			  struct work_struct *work)
> +{
> +	int cpu = cpumask_first(&wq_thread->cpus_allowed);
> +	struct cpu_workqueue_stats *node, *next;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +	list_for_each_entry_safe(node, next, &cpu_wq_list[cpu], list) {
> +		if (node->pid == wq_thread->pid) {
> +			atomic_inc(&node->inserted);
> +			goto found;
> +		}
> +	}
> +	pr_debug("trace_workqueue: entry not found\n");
> +found:
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +}
> +
> +/* Execution of a work */
> +static void
> +probe_workqueue_execution(struct task_struct *wq_thread,
> +			  struct work_struct *work)
> +{
> +	int cpu = cpumask_first(&wq_thread->cpus_allowed);
> +	struct cpu_workqueue_stats *node, *next;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +	list_for_each_entry_safe(node, next, &cpu_wq_list[cpu], list) {
> +		if (node->pid == wq_thread->pid) {
> +			node->executed++;
> +			goto found;
> +		}
> +	}
> +	pr_debug("trace_workqueue: entry not found\n");
> +found:
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +}
> +
> +/* Creation of a cpu workqueue thread */
> +static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
> +{
> +	struct cpu_workqueue_stats *cws;
> +	unsigned long flags;
> +
> +	WARN_ON(cpu < 0 || cpu >= NR_CPUS);
> +
> +	/* Workqueues are sometimes created in atomic context */
> +	cws = kzalloc(sizeof(struct cpu_workqueue_stats), GFP_ATOMIC);
> +	if (!cws) {
> +		pr_warning("trace_workqueue: not enough memory\n");
> +		return;
> +	}
> +	tracing_record_cmdline(wq_thread);
> +
> +	INIT_LIST_HEAD(&cws->list);
> +	cws->cpu = cpu;
> +
> +	cws->pid = wq_thread->pid;
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +	if (list_empty(&cpu_wq_list[cpu]))
> +		cws->first_entry = true;
> +	list_add_tail(&cws->list, &cpu_wq_list[cpu]);
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +}
> +
> +/* Destruction of a cpu workqueue thread */
> +static void probe_workqueue_destruction(struct task_struct *wq_thread)
> +{
> +	/* Workqueue only execute on one cpu */
> +	int cpu = cpumask_first(&wq_thread->cpus_allowed);
> +	struct cpu_workqueue_stats *node, *next;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +	list_for_each_entry_safe(node, next, &cpu_wq_list[cpu], list) {
> +		if (node->pid == wq_thread->pid) {
> +			list_del(&node->list);
> +			kfree(node);
> +			goto found;
> +		}
> +	}
> +
> +	pr_debug("trace_workqueue: don't find workqueue to destroy\n");
> +found:
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +
> +}
> +
> +static struct cpu_workqueue_stats *workqueue_stat_start_cpu(int cpu)
> +{
> +	unsigned long flags;
> +	struct cpu_workqueue_stats *ret = NULL;
> +
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +
> +	if (!list_empty(&cpu_wq_list[cpu]))
> +		ret = list_entry(cpu_wq_list[cpu].next,
> +				 struct cpu_workqueue_stats, list);
> +
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +
> +	return ret;
> +}
> +
> +static void *workqueue_stat_start(void)
> +{
> +	int i;
> +	void *ret = NULL;
> +
> +	for (i = 0; i < NR_CPUS; i++) {

Hi Frederic,

I'm getting these warnings from checkpatch.pl, and I think they are 
correct:

WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), 
num_possible_cpus(), for_each_possible_cpu(), etc
#953: FILE: kernel/trace/trace_workqueue.c:153:
+	for (i = 0; i < NR_CPUS; i++) {

We should probably change them to for_each_possible_cpu, or online cpu.

-- Steve

> +
> +		ret = workqueue_stat_start_cpu(i);
> +		if (ret)
> +			return ret;
> +	}
> +	return NULL;
> +}
> +
> +static void *workqueue_stat_next(void *prev, int idx)
> +{
> +	struct cpu_workqueue_stats *prev_cws = prev;
> +	int cpu = prev_cws->cpu;
> +	unsigned long flags;
> +	void *ret = NULL;
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +	if (list_is_last(&prev_cws->list, &cpu_wq_list[cpu])) {
> +		spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +		for (++cpu ; cpu < NR_CPUS; cpu++) {
> +			ret = workqueue_stat_start_cpu(cpu);
> +			if (ret)
> +				return ret;
> +		}
> +		return NULL;
> +	}
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +
> +	return list_entry(prev_cws->list.next, struct cpu_workqueue_stats,
> +			  list);
> +}
> +
> +static int workqueue_stat_show(struct seq_file *s, void *p)
> +{
> +	struct cpu_workqueue_stats *cws = p;
> +	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));
> +
> +	spin_lock_irqsave(&cpu_wq_list_lock[cpu], flags);
> +	if (&cws->list == cpu_wq_list[cpu].next)
> +		seq_printf(s, "\n");
> +	spin_unlock_irqrestore(&cpu_wq_list_lock[cpu], flags);
> +
> +	return 0;
> +}
> +
> +static int workqueue_stat_headers(struct seq_file *s)
> +{
> +	seq_printf(s, "# CPU  INSERTED  EXECUTED   NAME\n");
> +	seq_printf(s, "# |      |         |          |\n\n");
> +	return 0;
> +}
> +
> +struct tracer_stat workqueue_stats __read_mostly = {
> +	.name = "workqueues",
> +	.stat_start = workqueue_stat_start,
> +	.stat_next = workqueue_stat_next,
> +	.stat_show = workqueue_stat_show,
> +	.stat_headers = workqueue_stat_headers
> +};
> +
> +
> +int __init stat_workqueue_init(void)
> +{
> +	if (register_stat_tracer(&workqueue_stats)) {
> +		pr_warning("Unable to register workqueue stat tracer\n");
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +fs_initcall(stat_workqueue_init);
> +
> +/*
> + * Workqueues are created very early, just after pre-smp initcalls.
> + * So we must register our tracepoints at this stage.
> + */
> +int __init trace_workqueue_early_init(void)
> +{
> +	int ret, i;
> +
> +	ret = register_trace_workqueue_insertion(probe_workqueue_insertion);
> +	if (ret)
> +		goto out;
> +
> +	ret = register_trace_workqueue_execution(probe_workqueue_execution);
> +	if (ret)
> +		goto no_insertion;
> +
> +	ret = register_trace_workqueue_creation(probe_workqueue_creation);
> +	if (ret)
> +		goto no_execution;
> +
> +	ret = register_trace_workqueue_destruction(probe_workqueue_destruction);
> +	if (ret)
> +		goto no_creation;
> +
> +	for (i = 0; i < NR_CPUS; i++) {
> +		spin_lock_init(&cpu_wq_list_lock[i]);
> +		INIT_LIST_HEAD(&cpu_wq_list[i]);
> +	}
> +
> +	return 0;
> +
> +no_creation:
> +	unregister_trace_workqueue_creation(probe_workqueue_creation);
> +no_execution:
> +	unregister_trace_workqueue_execution(probe_workqueue_execution);
> +no_insertion:
> +	unregister_trace_workqueue_insertion(probe_workqueue_insertion);
> +out:
> +	pr_warning("trace_workqueue: unable to trace workqueues\n");
> +
> +	return 1;
> +}
> +early_initcall(trace_workqueue_early_init);
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 2f44583..71145f8 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -33,6 +33,7 @@
>  #include <linux/kallsyms.h>
>  #include <linux/debug_locks.h>
>  #include <linux/lockdep.h>
> +#include <trace/workqueue.h>
>  
>  /*
>   * The per-CPU workqueue (if single thread, we always use the first
> @@ -138,11 +139,15 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
>  	wake_up(&cwq->more_work);
>  }
>  
> +DEFINE_TRACE(workqueue_insertion);
> +
>  static void __queue_work(struct cpu_workqueue_struct *cwq,
>  			 struct work_struct *work)
>  {
>  	unsigned long flags;
>  
> +	trace_workqueue_insertion(cwq->thread, work);
> +
>  	spin_lock_irqsave(&cwq->lock, flags);
>  	insert_work(cwq, work, &cwq->worklist);
>  	spin_unlock_irqrestore(&cwq->lock, flags);
> @@ -259,6 +264,8 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
>  }
>  EXPORT_SYMBOL_GPL(queue_delayed_work_on);
>  
> +DEFINE_TRACE(workqueue_execution);
> +
>  static void run_workqueue(struct cpu_workqueue_struct *cwq)
>  {
>  	spin_lock_irq(&cwq->lock);
> @@ -284,7 +291,7 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
>  		 */
>  		struct lockdep_map lockdep_map = work->lockdep_map;
>  #endif
> -
> +		trace_workqueue_execution(cwq->thread, work);
>  		cwq->current_work = work;
>  		list_del_init(cwq->worklist.next);
>  		spin_unlock_irq(&cwq->lock);
> @@ -765,6 +772,8 @@ init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
>  	return cwq;
>  }
>  
> +DEFINE_TRACE(workqueue_creation);
> +
>  static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
>  {
>  	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
> @@ -787,6 +796,8 @@ 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);
> +
>  	return 0;
>  }
>  
> @@ -868,6 +879,8 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
>  }
>  EXPORT_SYMBOL_GPL(__create_workqueue_key);
>  
> +DEFINE_TRACE(workqueue_destruction);
> +
>  static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
>  {
>  	/*
> @@ -891,6 +904,7 @@ 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);
>  	kthread_stop(cwq->thread);
>  	cwq->thread = NULL;
>  }
> -- 
> 1.6.0.4
> 
> 
> 
> 
--
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