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    SubjectRe: [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@gmail.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@gmail.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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