[RFC/PATCH] trace: Remove unused workqueue tracer

[Stephen Boyd <sboyd@codeaurora.org>]

This tracer was temporarily removed in 6416669 (workqueue:
temporarily remove workqueue tracing, 2010-06-29) but never
reinstated after concurrency managed workqueues were completed.
For almost two years it hasn't been compilable so it seems nobody
is using it. Delete it.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---

I noticed this while poking through the tracer code. This patch
is meant to incite discussion.

Can this tracer be salvaged? In it's simplest form I suppose we can
trace the number of queued, active, running, and completed work items.

 kernel/trace/Makefile          |    1 -
 kernel/trace/trace_workqueue.c |  300 ----------------------------------------
 2 files changed, 301 deletions(-)
 delete mode 100644 kernel/trace/trace_workqueue.c

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 5f39a07..b3afe0e 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -41,7 +41,6 @@ obj-$(CONFIG_STACK_TRACER) += trace_stack.o
 obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += trace_functions_graph.o
 obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
-obj-$(CONFIG_WORKQUEUE_TRACER) += trace_workqueue.o
 obj-$(CONFIG_BLK_DEV_IO_TRACE) += blktrace.o
 ifeq ($(CONFIG_BLOCK),y)
 obj-$(CONFIG_EVENT_TRACING) += blktrace.o
diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
deleted file mode 100644
index 209b379..0000000
--- a/kernel/trace/trace_workqueue.c
+++ /dev/null
@@ -1,300 +0,0 @@
-/*
- * Workqueue statistical tracer.
- *
- * Copyright (C) 2008 Frederic Weisbecker <fweisbec@gmail.com>
- *
- */
-
-
-#include <trace/events/workqueue.h>
-#include <linux/list.h>
-#include <linux/percpu.h>
-#include <linux/slab.h>
-#include <linux/kref.h>
-#include "trace_stat.h"
-#include "trace.h"
-
-
-/* A cpu workqueue thread */
-struct cpu_workqueue_stats {
-	struct list_head            list;
-	struct kref                 kref;
-	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;
-};
-
-/* List of workqueue threads on one cpu */
-struct workqueue_global_stats {
-	struct list_head	list;
-	spinlock_t		lock;
-};
-
-/* Don't need a global lock because allocated before the workqueues, and
- * never freed.
- */
-static DEFINE_PER_CPU(struct workqueue_global_stats, all_workqueue_stat);
-#define workqueue_cpu_stat(cpu) (&per_cpu(all_workqueue_stat, cpu))
-
-static void cpu_workqueue_stat_free(struct kref *kref)
-{
-	kfree(container_of(kref, struct cpu_workqueue_stats, kref));
-}
-
-/* Insertion of a work */
-static void
-probe_workqueue_insertion(void *ignore,
-			  struct task_struct *wq_thread,
-			  struct work_struct *work)
-{
-	int cpu = cpumask_first(&wq_thread->cpus_allowed);
-	struct cpu_workqueue_stats *node;
-	unsigned long flags;
-
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_for_each_entry(node, &workqueue_cpu_stat(cpu)->list, 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(&workqueue_cpu_stat(cpu)->lock, flags);
-}
-
-/* Execution of a work */
-static void
-probe_workqueue_execution(void *ignore,
-			  struct task_struct *wq_thread,
-			  struct work_struct *work)
-{
-	int cpu = cpumask_first(&wq_thread->cpus_allowed);
-	struct cpu_workqueue_stats *node;
-	unsigned long flags;
-
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_for_each_entry(node, &workqueue_cpu_stat(cpu)->list, list) {
-		if (node->pid == wq_thread->pid) {
-			node->executed++;
-			goto found;
-		}
-	}
-	pr_debug("trace_workqueue: entry not found\n");
-found:
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
-}
-
-/* Creation of a cpu workqueue thread */
-static void probe_workqueue_creation(void *ignore,
-				     struct task_struct *wq_thread, int cpu)
-{
-	struct cpu_workqueue_stats *cws;
-	unsigned long flags;
-
-	WARN_ON(cpu < 0);
-
-	/* 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;
-	}
-	INIT_LIST_HEAD(&cws->list);
-	kref_init(&cws->kref);
-	cws->cpu = cpu;
-	cws->pid = wq_thread->pid;
-
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_add_tail(&cws->list, &workqueue_cpu_stat(cpu)->list);
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
-}
-
-/* Destruction of a cpu workqueue thread */
-static void
-probe_workqueue_destruction(void *ignore, 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(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
-							list) {
-		if (node->pid == wq_thread->pid) {
-			list_del(&node->list);
-			kref_put(&node->kref, cpu_workqueue_stat_free);
-			goto found;
-		}
-	}
-
-	pr_debug("trace_workqueue: don't find workqueue to destroy\n");
-found:
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
-
-}
-
-static struct cpu_workqueue_stats *workqueue_stat_start_cpu(int cpu)
-{
-	unsigned long flags;
-	struct cpu_workqueue_stats *ret = NULL;
-
-
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-
-	if (!list_empty(&workqueue_cpu_stat(cpu)->list)) {
-		ret = list_entry(workqueue_cpu_stat(cpu)->list.next,
-				 struct cpu_workqueue_stats, list);
-		kref_get(&ret->kref);
-	}
-
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
-
-	return ret;
-}
-
-static void *workqueue_stat_start(struct tracer_stat *trace)
-{
-	int cpu;
-	void *ret = NULL;
-
-	for_each_possible_cpu(cpu) {
-		ret = workqueue_stat_start_cpu(cpu);
-		if (ret)
-			return ret;
-	}
-	return NULL;
-}
-
-static void *workqueue_stat_next(void *prev, int idx)
-{
-	struct cpu_workqueue_stats *prev_cws = prev;
-	struct cpu_workqueue_stats *ret;
-	int cpu = prev_cws->cpu;
-	unsigned long flags;
-
-	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);
-		do {
-			cpu = cpumask_next(cpu, cpu_possible_mask);
-			if (cpu >= nr_cpu_ids)
-				return NULL;
-		} while (!(ret = workqueue_stat_start_cpu(cpu)));
-		return ret;
-	} else {
-		ret = list_entry(prev_cws->list.next,
-				 struct cpu_workqueue_stats, list);
-		kref_get(&ret->kref);
-	}
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
-
-	return ret;
-}
-
-static int workqueue_stat_show(struct seq_file *s, void *p)
-{
-	struct cpu_workqueue_stats *cws = p;
-	struct pid *pid;
-	struct task_struct *tsk;
-
-	pid = find_get_pid(cws->pid);
-	if (pid) {
-		tsk = get_pid_task(pid, PIDTYPE_PID);
-		if (tsk) {
-			seq_printf(s, "%3d %6d     %6u       %s\n", cws->cpu,
-				   atomic_read(&cws->inserted), cws->executed,
-				   tsk->comm);
-			put_task_struct(tsk);
-		}
-		put_pid(pid);
-	}
-
-	return 0;
-}
-
-static void workqueue_stat_release(void *stat)
-{
-	struct cpu_workqueue_stats *node = stat;
-
-	kref_put(&node->kref, cpu_workqueue_stat_free);
-}
-
-static int workqueue_stat_headers(struct seq_file *s)
-{
-	seq_printf(s, "# CPU  INSERTED  EXECUTED   NAME\n");
-	seq_printf(s, "# |      |         |          |\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_release = workqueue_stat_release,
-	.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, cpu;
-
-	for_each_possible_cpu(cpu) {
-		spin_lock_init(&workqueue_cpu_stat(cpu)->lock);
-		INIT_LIST_HEAD(&workqueue_cpu_stat(cpu)->list);
-	}
-
-	ret = register_trace_workqueue_insertion(probe_workqueue_insertion, NULL);
-	if (ret)
-		goto out;
-
-	ret = register_trace_workqueue_execution(probe_workqueue_execution, NULL);
-	if (ret)
-		goto no_insertion;
-
-	ret = register_trace_workqueue_creation(probe_workqueue_creation, NULL);
-	if (ret)
-		goto no_execution;
-
-	ret = register_trace_workqueue_destruction(probe_workqueue_destruction, NULL);
-	if (ret)
-		goto no_creation;
-
-	return 0;
-
-no_creation:
-	unregister_trace_workqueue_creation(probe_workqueue_creation, NULL);
-no_execution:
-	unregister_trace_workqueue_execution(probe_workqueue_execution, NULL);
-no_insertion:
-	unregister_trace_workqueue_insertion(probe_workqueue_insertion, NULL);
-out:
-	pr_warning("trace_workqueue: unable to trace workqueues\n");
-
-	return 1;
-}
-early_initcall(trace_workqueue_early_init);
-- 
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The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.