Commit c3ffc7a4 authored by KOSAKI Motohiro's avatar KOSAKI Motohiro Committed by Ingo Molnar

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: default avatarKOSAKI 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: default avatarIngo Molnar <mingo@elte.hu>
parent 888b55dc
...@@ -99,8 +99,6 @@ static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu) ...@@ -99,8 +99,6 @@ static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
pr_warning("trace_workqueue: not enough memory\n"); pr_warning("trace_workqueue: not enough memory\n");
return; return;
} }
tracing_record_cmdline(wq_thread);
INIT_LIST_HEAD(&cws->list); INIT_LIST_HEAD(&cws->list);
cws->cpu = cpu; cws->cpu = cpu;
...@@ -195,11 +193,12 @@ static int workqueue_stat_show(struct seq_file *s, void *p) ...@@ -195,11 +193,12 @@ static int workqueue_stat_show(struct seq_file *s, void *p)
struct cpu_workqueue_stats *cws = p; struct cpu_workqueue_stats *cws = p;
unsigned long flags; unsigned long flags;
int cpu = cws->cpu; int cpu = cws->cpu;
struct task_struct *tsk = find_task_by_vpid(cws->pid);
seq_printf(s, "%3d %6d %6u %s\n", cws->cpu, seq_printf(s, "%3d %6d %6u %s\n", cws->cpu,
atomic_read(&cws->inserted), atomic_read(&cws->inserted),
cws->executed, cws->executed,
trace_find_cmdline(cws->pid)); tsk ? tsk->comm : "<...>");
spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags); spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
if (&cws->list == workqueue_cpu_stat(cpu)->list.next) if (&cws->list == workqueue_cpu_stat(cpu)->list.next)
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment