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authorKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>2009-03-09 18:15:34 +0900
committerIngo Molnar <mingo@elte.hu>2009-03-09 10:26:13 +0100
commitc3ffc7a40b7e94b094efe1c8ab4e24370a782b65 (patch)
tree13e2831b866f1ee2ff1bc395400c87e2980225eb
parent888b55dc314d26239d84c3b187dae555a81c1605 (diff)
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tracing: Don't use tracing_record_cmdline() in workqueue tracer
Impact: improve workqueue tracer output Currently, /sys/kernel/debug/tracing/trace_stat/workqueues can display wrong and strange thread names. Why? Currently, ftrace has tracing_record_cmdline()/trace_find_cmdline() convenience function that implements a task->comm string cache. This can avoid unnecessary memcpy overhead and the workqueue tracer uses it. However, in general, any trace statistics feature shouldn't use tracing_record_cmdline() because trace statistics can display very old process. Then comm cache can return wrong string because recent process overrides the cache. Fortunately, workqueue trace guarantees that displayed processes are live. Thus we can search comm string from PID at display time. <before> % cat workqueues # CPU INSERTED EXECUTED NAME # | | | | 7 431913 431913 kondemand/7 7 0 0 tail 7 21 21 git 7 0 0 ls 7 9 9 cat 7 832632 832632 unix_chkpwd 7 236292 236292 ls Note: tail, git, ls, cat unix_chkpwd are obiously not workqueue thread. <after> % cat workqueues # CPU INSERTED EXECUTED NAME # | | | | 7 510 510 kondemand/7 7 0 0 kmpathd/7 7 15 15 ata/7 7 0 0 aio/7 7 11 11 kblockd/7 7 1063 1063 work_on_cpu/7 7 167 167 events/7 Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Steven Rostedt <srostedt@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/trace/trace_workqueue.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
index 4664990fe9c..46c8dc896bd 100644
--- a/kernel/trace/trace_workqueue.c
+++ b/kernel/trace/trace_workqueue.c
@@ -99,8 +99,6 @@ static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
pr_warning("trace_workqueue: not enough memory\n");
return;
}
- tracing_record_cmdline(wq_thread);
-
INIT_LIST_HEAD(&cws->list);
cws->cpu = cpu;
@@ -195,11 +193,12 @@ static int workqueue_stat_show(struct seq_file *s, void *p)
struct cpu_workqueue_stats *cws = p;
unsigned long flags;
int cpu = cws->cpu;
+ struct task_struct *tsk = find_task_by_vpid(cws->pid);
seq_printf(s, "%3d %6d %6u %s\n", cws->cpu,
atomic_read(&cws->inserted),
cws->executed,
- trace_find_cmdline(cws->pid));
+ tsk ? tsk->comm : "<...>");
spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
if (&cws->list == workqueue_cpu_stat(cpu)->list.next)