[PATCH] distinct tgid/tid I/O statistics (was: taskstats and /proc/.../io asymmetry?)

[Andrea Righi <righiandr@users.sourceforge.net>]

Balbir Singh wrote:
> Mark Seger wrote:
>> If you look at /proc/pid/stat, you can get the total CPU consumed by a
>> process.  If you look at /proc/pid/task/tid/stat you can get the cpu
>> consumed by a thread and if the tid is that of the parent you only gets
>> its consumption as opposed to all its children.
>>
>> I was surprised to see that the way process I/O is reported doesn't
>> follow this model.  There are no /prod/pid/task/tid/io entries but
>> rather you need to look in /proc/tid/io.  While I view this as a minor
>> inconvenience, I can certainly live with it.  However, /proc/pid/io does
>> not show the aggregate I/O numbers for the whole process and that both
>> surprises and disappoints.  This means if I have a process that starts a
>> bunch of worker threads that do the real work and I want to find the top
>> I/O consumers I can't simply walk the /proc/pid tree but rather have to
>> look at all the threads of each process and add them up.
>>
>> Or am I missing something?
>>
> 
> I looked through the code and your argument seems to be correct. The behaviour
> is inconsistent w.r.t. other statistics like utime and stime. We currently
> accumulate tgid information in signal_struct, we need to do something similar
> for io as well. If nobody gets to it by the time I finish my backlog, I'll try
> and get to it.

Balbir, Mark,

what do you think about the following approach?
Patch against 2.6.25.4, tested in KVM.

-Andrea

--
Report per-thread I/O statistics in /proc/pid/task/tid/io and aggregate
parent I/O statistics in /proc/pid/io. This approach follows the same
model used to account per-process and per-thread CPU times.

As a practial application, this allows for example to quickly find the
top I/O consumer when a process spawns many child threads that perform
the actual I/O work, because the aggregated I/O statistics can always be
found in /proc/pid/io.

Bug reported by Mark Seger <Mark.Seger@hp.com>.

Signed-off-by: Andrea Righi <righiandr@users.sourceforge.net>
---
 fs/proc/base.c        |   83 +++++++++++++++++++++++++++++++++++++++++++------
 include/linux/sched.h |    4 ++
 kernel/exit.c         |   27 ++++++++++++++++
 kernel/fork.c         |    6 +++
 4 files changed, 110 insertions(+), 10 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 81d7d14..23763c5 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2255,8 +2255,58 @@ static int proc_base_fill_cache(struct file *filp, void *dirent,
 }
 
 #ifdef CONFIG_TASK_IO_ACCOUNTING
-static int proc_pid_io_accounting(struct task_struct *task, char *buffer)
+static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
 {
+	unsigned long flags;
+	u64 rchar, wchar, syscr, syscw;
+	struct task_io_accounting ioac;
+
+	if (!whole) {
+#ifdef CONFIG_TASK_XACCT
+		rchar = task->rchar;
+		wchar = task->wchar;
+		syscr = task->syscr;
+		syscw = task->syscw;
+#endif
+		memcpy(&ioac, &task->ioac, sizeof(ioac));
+	} else {
+		rchar = wchar = syscr = syscw = 0;
+		memset(&ioac, 0, sizeof(ioac));
+		rcu_read_lock();
+		if (lock_task_sighand(task, &flags)) {
+		struct signal_struct *sig = task->signal;
+		struct task_struct *t = task;
+
+			do {
+#ifdef CONFIG_TASK_XACCT
+				rchar += t->rchar;
+				wchar += t->wchar;
+				syscr += t->syscr;
+				syscw += t->syscw;
+#endif
+				ioac.read_bytes += t->ioac.read_bytes;
+				ioac.write_bytes += t->ioac.write_bytes;
+				ioac.cancelled_write_bytes +=
+						t->ioac.cancelled_write_bytes;
+				t = next_thread(t);
+			} while (t != task);
+
+#ifdef CONFIG_TASK_XACCT
+			rchar += sig->rchar;
+			wchar += sig->wchar;
+			syscr += sig->syscr;
+			syscw += sig->syscw;
+#endif
+			ioac.read_bytes += sig->ioac.read_bytes;
+			ioac.write_bytes += sig->ioac.write_bytes;
+			ioac.cancelled_write_bytes +=
+					sig->ioac.cancelled_write_bytes;
+
+			unlock_task_sighand(task, &flags);
+		}
+		rcu_read_unlock();
+	}
+
 	return sprintf(buffer,
 #ifdef CONFIG_TASK_XACCT
 			"rchar: %llu\n"
@@ -2268,16 +2318,26 @@ static int proc_pid_io_accounting(struct task_struct *task, char *buffer)
 			"write_bytes: %llu\n"
 			"cancelled_write_bytes: %llu\n",
 #ifdef CONFIG_TASK_XACCT
-			(unsigned long long)task->rchar,
-			(unsigned long long)task->wchar,
-			(unsigned long long)task->syscr,
-			(unsigned long long)task->syscw,
+			(unsigned long long)rchar,
+			(unsigned long long)wchar,
+			(unsigned long long)syscr,
+			(unsigned long long)syscw,
 #endif
-			(unsigned long long)task->ioac.read_bytes,
-			(unsigned long long)task->ioac.write_bytes,
-			(unsigned long long)task->ioac.cancelled_write_bytes);
+			(unsigned long long)ioac.read_bytes,
+			(unsigned long long)ioac.write_bytes,
+			(unsigned long long)ioac.cancelled_write_bytes);
+}
+
+static int proc_tid_io_accounting(struct task_struct *task, char *buffer)
+{
+	return do_io_accounting(task, buffer, 0);
 }
-#endif
+
+static int proc_tgid_io_accounting(struct task_struct *task, char *buffer)
+{
+	return do_io_accounting(task, buffer, 1);
+}
+#endif /* CONFIG_TASK_IO_ACCOUNTING */
 
 /*
  * Thread groups
@@ -2348,7 +2408,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 	REG("coredump_filter", S_IRUGO|S_IWUSR, coredump_filter),
 #endif
 #ifdef CONFIG_TASK_IO_ACCOUNTING
-	INF("io",	S_IRUGO, pid_io_accounting),
+	INF("io",	S_IRUGO, tgid_io_accounting),
 #endif
 };
 
@@ -2675,6 +2735,9 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_FAULT_INJECTION
 	REG("make-it-fail", S_IRUGO|S_IWUSR, fault_inject),
 #endif
+#ifdef CONFIG_TASK_IO_ACCOUNTING
+	INF("io",	S_IRUGO, tid_io_accounting),
+#endif
 };
 
 static int proc_tid_base_readdir(struct file * filp,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6a1e7af..ebf8b45 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -504,6 +504,10 @@ struct signal_struct {
 	unsigned long nvcsw, nivcsw, cnvcsw, cnivcsw;
 	unsigned long min_flt, maj_flt, cmin_flt, cmaj_flt;
 	unsigned long inblock, oublock, cinblock, coublock;
+#ifdef CONFIG_TASK_XACCT
+	u64 rchar, wchar, syscr, syscw;
+#endif
+	struct task_io_accounting ioac;
 
 	/*
 	 * Cumulative ns of scheduled CPU time for dead threads in the
diff --git a/kernel/exit.c b/kernel/exit.c
index 073005b..1a35583 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -114,6 +114,18 @@ static void __exit_signal(struct task_struct *tsk)
 		sig->nivcsw += tsk->nivcsw;
 		sig->inblock += task_io_get_inblock(tsk);
 		sig->oublock += task_io_get_oublock(tsk);
+#ifdef CONFIG_TASK_XACCT
+		sig->rchar += tsk->rchar;
+		sig->wchar += tsk->wchar;
+		sig->syscr += tsk->syscr;
+		sig->syscw += tsk->syscw;
+#endif /* CONFIG_TASK_XACCT */
+#ifdef CONFIG_TASK_IO_ACCOUNTING
+		sig->ioac.read_bytes += tsk->ioac.read_bytes;
+		sig->ioac.write_bytes += tsk->ioac.write_bytes;
+		sig->ioac.cancelled_write_bytes +=
+					tsk->ioac.cancelled_write_bytes;
+#endif /* CONFIG_TASK_IO_ACCOUNTING */
 		sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
 		sig = NULL; /* Marker for below. */
 	}
@@ -1250,6 +1262,21 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
 		psig->coublock +=
 			task_io_get_oublock(p) +
 			sig->oublock + sig->coublock;
+#ifdef CONFIG_TASK_XACCT
+		psig->rchar += p->rchar + sig->rchar;
+		psig->wchar += p->wchar + sig->wchar;
+		psig->syscr += p->syscr + sig->syscr;
+		psig->syscw += p->syscw + sig->syscw;
+#endif /* CONFIG_TASK_XACCT */
+#ifdef CONFIG_TASK_IO_ACCOUNTING
+		psig->ioac.read_bytes +=
+			p->ioac.read_bytes + sig->ioac.read_bytes;
+		psig->ioac.write_bytes +=
+			p->ioac.write_bytes + sig->ioac.write_bytes;
+		psig->ioac.cancelled_write_bytes +=
+				p->ioac.cancelled_write_bytes +
+				sig->ioac.cancelled_write_bytes;
+#endif /* CONFIG_TASK_IO_ACCOUNTING */
 		spin_unlock_irq(&p->parent->sighand->siglock);
 	}
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 9c042f9..b8f408e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -924,6 +924,12 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 	sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
 	sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
 	sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
+#ifdef CONFIG_TASK_XACCT
+	sig->rchar = sig->wchar = sig->syscr = sig->syscw = 0;
+#endif
+#ifdef CONFIG_TASK_IO_ACCOUNTING
+	memset(&sig->ioac, 0, sizeof(sig->ioac));
+#endif
 	sig->sum_sched_runtime = 0;
 	INIT_LIST_HEAD(&sig->cpu_timers[0]);
 	INIT_LIST_HEAD(&sig->cpu_timers[1]);
-- 
1.5.4.3