[PATCH 0/3] Teach perf_trace_##call() to check hlist_empty(perf_events)

[PATCH 0/3] Teach perf_trace_##call() to check hlist_empty(perf_events)

[Oleg Nesterov]

Sorry for double post, forgot to cc lkml...

On 07/19, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@redhat.com> wrote:
>
> > Hello.
> >
> > The patches are the same, I only tried to update the changelogs a bit.
> > I am also quoting my old email below, to explain what this hack tries
> > to do.
> >
> > 	Say, "perf record -e sched:sched_switch -p1".
> >
> > 	Every task except /sbin/init will do perf_trace_sched_switch() and
> > 	perf_trace_buf_prepare() + perf_trace_buf_submit for no reason(),
> > 	it doesn't have a counter.
> >
> > 	So it makes sense to add the fast-path check at the start of
> > 	perf_trace_##call(),
> >
> > 		if (hlist_empty(event_call->perf_events))
> > 			return;
> >
> > 	The problem is, we should not do this if __task != NULL (iow, if
> > 	DECLARE_EVENT_CLASS() uses __perf_task()), perf_tp_event() has the
> > 	additional code for this case.
> >
> > 	So we should do
> >
> > 		if (!__task && hlist_empty(event_call->perf_events))
> > 			return;
> >
> > 	But __task is changed by "{ assign; }" block right before
> > 	perf_trace_buf_submit(). Too late for the fast-path check,
> > 	we already called perf_trace_buf_prepare/fetch_regs.
> >
> > 	So. After 2/3 __perf_task() (and __perf_count/addr) is called
> > 	when ftrace_get_offsets_##call(args) evaluates the arguments,
> > 	and we can check !__task && hlist_empty() right after that.
> >
> > Oleg.
>
> Nice improvement.
>
> Peter, Steve, any objections?

Ingo,

It seems that everybody agree with this hack but it was forgotten,
let me resend it again.

The only change is that I added the following tags:

	Tested-by: David Ahern <dsahern@gmail.com>
	Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>

Oleg.

 include/trace/events/sched.h |   22 ++++++++--------------
 include/trace/ftrace.h       |   33 ++++++++++++++++++++-------------
 2 files changed, 28 insertions(+), 27 deletions(-)

[PATCH 1/3] tracing/perf: Expand TRACE_EVENT(sched_stat_runtime)

[Oleg Nesterov]

To simplify the review of the next patches:

1. We are going to reimplent __perf_task/counter and embedd them
   into TP_ARGS(). expand TRACE_EVENT(sched_stat_runtime) into
   DECLARE_EVENT_CLASS() + DEFINE_EVENT(), this way they can use
   different TP_ARGS's.

2. Change perf_trace_##call() macro to do perf_fetch_caller_regs()
   right before perf_trace_buf_prepare().

   This way it evaluates TP_ARGS() asap, the next patch explores
   this fact.

   Note: after 87f44bbc perf_trace_buf_prepare() doesn't need
   "struct pt_regs *regs", perhaps it makes sense to remove this
   argument. And perhaps we can teach perf_trace_buf_submit()
   to accept regs == NULL and do fetch_caller_regs(CALLER_ADDR1)
   in this case.

3. Cosmetic, but the typecast from "void*" buys nothing. It just
   adds the noise, remove it.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: David Ahern <dsahern@gmail.com>
Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/trace/events/sched.h |    6 +++++-
 include/trace/ftrace.h       |    7 +++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index e5586ca..249c024 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -372,7 +372,7 @@ DEFINE_EVENT(sched_stat_template, sched_stat_blocked,
  * Tracepoint for accounting runtime (time the task is executing
  * on a CPU).
  */
-TRACE_EVENT(sched_stat_runtime,
+DECLARE_EVENT_CLASS(sched_stat_runtime,
 
 	TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),
 
@@ -401,6 +401,10 @@ TRACE_EVENT(sched_stat_runtime,
 			(unsigned long long)__entry->vruntime)
 );
 
+DEFINE_EVENT(sched_stat_runtime, sched_stat_runtime,
+	     TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),
+	     TP_ARGS(tsk, runtime, vruntime));
+
 /*
  * Tracepoint for showing priority inheritance modifying a tasks
  * priority.
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 41a6643..618af05 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -663,15 +663,14 @@ perf_trace_##call(void *__data, proto)					\
 	int __data_size;						\
 	int rctx;							\
 									\
-	perf_fetch_caller_regs(&__regs);				\
-									\
 	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
 	__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
 			     sizeof(u64));				\
 	__entry_size -= sizeof(u32);					\
 									\
-	entry = (struct ftrace_raw_##call *)perf_trace_buf_prepare(	\
-		__entry_size, event_call->event.type, &__regs, &rctx);	\
+	perf_fetch_caller_regs(&__regs);				\
+	entry = perf_trace_buf_prepare(__entry_size,			\
+			event_call->event.type, &__regs, &rctx);	\
 	if (!entry)							\
 		return;							\
 									\
-- 
1.5.5.1

Re: [PATCH 1/3] tracing/perf: Expand TRACE_EVENT(sched_stat_runtime)

[Steven Rostedt]

On Mon, 2013-08-05 at 18:50 +0200, Oleg Nesterov wrote:

> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Tested-by: David Ahern <dsahern@gmail.com>
> Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>

Just so you know. The standard that we now want to live by is only one
tag per line. I know I gave you that tag in my email, but when adding it
to a patch it needs to be:

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>

I wonder if the Reviewed-by assumes the Acked-by? Anyway, if you add
both, it needs to be like that.

-- Steve

Re: [PATCH 1/3] tracing/perf: Expand TRACE_EVENT(sched_stat_runtime)

[Oleg Nesterov]

On 08/05, Steven Rostedt wrote:
>
> On Mon, 2013-08-05 at 18:50 +0200, Oleg Nesterov wrote:
>
> > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> > Tested-by: David Ahern <dsahern@gmail.com>
> > Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>
>
> Just so you know. The standard that we now want to live by is only one
> tag per line. I know I gave you that tag in my email, but when adding it
> to a patch it needs to be:
>
> Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
> Acked-by: Steven Rostedt <rostedt@goodmis.org>
>
> I wonder if the Reviewed-by assumes the Acked-by? Anyway, if you add
> both, it needs to be like that.

Sorry... should I resend once again ?

Oleg.

Re: [PATCH 1/3] tracing/perf: Expand TRACE_EVENT(sched_stat_runtime)

[Steven Rostedt]

On Mon, 2013-08-05 at 20:51 +0200, Oleg Nesterov wrote:
> On 08/05, Steven Rostedt wrote:
> >
> > On Mon, 2013-08-05 at 18:50 +0200, Oleg Nesterov wrote:
> >
> > > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> > > Tested-by: David Ahern <dsahern@gmail.com>
> > > Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>
> >
> > Just so you know. The standard that we now want to live by is only one
> > tag per line. I know I gave you that tag in my email, but when adding it
> > to a patch it needs to be:
> >
> > Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
> > Acked-by: Steven Rostedt <rostedt@goodmis.org>
> >
> > I wonder if the Reviewed-by assumes the Acked-by? Anyway, if you add
> > both, it needs to be like that.
> 
> Sorry... should I resend once again ?
> 

Sure, why not. It's only 3 patches :-)

-- Steve

[PATCH 2/3] tracing/perf: Reimplement TP_perf_assign() logic

[Oleg Nesterov]

The next patch tries to avoid the costly perf_trace_buf_* calls
when possible but there is a problem. We can only do this if
__task == NULL, perf_tp_event(task != NULL) has the additional
code for this case.

Unfortunately, TP_perf_assign/__perf_xxx which changes the default
values of __count/__task variables for perf_trace_buf_submit() is
called "too late", after we already did perf_trace_buf_prepare(),
and the optimization above can't work.

So this patch simply embeds __perf_xxx() into TP_ARGS(), this way
DECLARE_EVENT_CLASS() can use the result of assignments hidden in
"args" right after ftrace_get_offsets_##call() which is mostly
trivial. This allows us to have the fast-path "__task != NULL"
check at the start, see the next patch.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: David Ahern <dsahern@gmail.com>
Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/trace/events/sched.h |   16 +++-------------
 include/trace/ftrace.h       |   19 +++++++++++--------
 2 files changed, 14 insertions(+), 21 deletions(-)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 249c024..2e7d994 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -57,7 +57,7 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
 
 	TP_PROTO(struct task_struct *p, int success),
 
-	TP_ARGS(p, success),
+	TP_ARGS(__perf_task(p), success),
 
 	TP_STRUCT__entry(
 		__array(	char,	comm,	TASK_COMM_LEN	)
@@ -73,9 +73,6 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
 		__entry->prio		= p->prio;
 		__entry->success	= success;
 		__entry->target_cpu	= task_cpu(p);
-	)
-	TP_perf_assign(
-		__perf_task(p);
 	),
 
 	TP_printk("comm=%s pid=%d prio=%d success=%d target_cpu=%03d",
@@ -313,7 +310,7 @@ DECLARE_EVENT_CLASS(sched_stat_template,
 
 	TP_PROTO(struct task_struct *tsk, u64 delay),
 
-	TP_ARGS(tsk, delay),
+	TP_ARGS(__perf_task(tsk), __perf_count(delay)),
 
 	TP_STRUCT__entry(
 		__array( char,	comm,	TASK_COMM_LEN	)
@@ -325,10 +322,6 @@ DECLARE_EVENT_CLASS(sched_stat_template,
 		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
 		__entry->pid	= tsk->pid;
 		__entry->delay	= delay;
-	)
-	TP_perf_assign(
-		__perf_count(delay);
-		__perf_task(tsk);
 	),
 
 	TP_printk("comm=%s pid=%d delay=%Lu [ns]",
@@ -376,7 +369,7 @@ DECLARE_EVENT_CLASS(sched_stat_runtime,
 
 	TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),
 
-	TP_ARGS(tsk, runtime, vruntime),
+	TP_ARGS(tsk, __perf_count(runtime), vruntime),
 
 	TP_STRUCT__entry(
 		__array( char,	comm,	TASK_COMM_LEN	)
@@ -390,9 +383,6 @@ DECLARE_EVENT_CLASS(sched_stat_runtime,
 		__entry->pid		= tsk->pid;
 		__entry->runtime	= runtime;
 		__entry->vruntime	= vruntime;
-	)
-	TP_perf_assign(
-		__perf_count(runtime);
 	),
 
 	TP_printk("comm=%s pid=%d runtime=%Lu [ns] vruntime=%Lu [ns]",
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 618af05..4163d93 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -507,8 +507,14 @@ static inline notrace int ftrace_get_offsets_##call(			\
 #undef TP_fast_assign
 #define TP_fast_assign(args...) args
 
-#undef TP_perf_assign
-#define TP_perf_assign(args...)
+#undef __perf_addr
+#define __perf_addr(a)	(a)
+
+#undef __perf_count
+#define __perf_count(c)	(c)
+
+#undef __perf_task
+#define __perf_task(t)	(t)
 
 #undef DECLARE_EVENT_CLASS
 #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
@@ -636,16 +642,13 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
 #define __get_str(field) (char *)__get_dynamic_array(field)
 
 #undef __perf_addr
-#define __perf_addr(a) __addr = (a)
+#define __perf_addr(a)	(__addr = (a))
 
 #undef __perf_count
-#define __perf_count(c) __count = (c)
+#define __perf_count(c)	(__count = (c))
 
 #undef __perf_task
-#define __perf_task(t) __task = (t)
-
-#undef TP_perf_assign
-#define TP_perf_assign(args...) args
+#define __perf_task(t)	(__task = (t))
 
 #undef DECLARE_EVENT_CLASS
 #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
-- 
1.5.5.1

[PATCH 3/3] tracing/perf: Avoid perf_trace_buf_*() in perf_trace_##call() when possible

[Oleg Nesterov]

perf_trace_buf_prepare() + perf_trace_buf_submit(task => NULL)
make no sense if hlist_empty(head). Change perf_trace_##call()
to check ->perf_events beforehand and do nothing if it is empty.

This removes the overhead for tasks without events associated
with them. For example, "perf record -e sched:sched_switch -p1"
attaches the counter(s) to the single task, but every task in
system will do perf_trace_buf_prepare/submit() just to realize
that it was not attached to this event.

However, we can only do this if __task == NULL, so we also add
the __builtin_constant_p(__task) check.

With this patch "perf bench sched pipe" shows approximately 4%
improvement when "perf record -p1" runs in parallel, many thanks
to Steven for the testing.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: David Ahern <dsahern@gmail.com>
Reviewed-and-Acked-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/trace/ftrace.h |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 4163d93..5c7ab17 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -667,6 +667,12 @@ perf_trace_##call(void *__data, proto)					\
 	int rctx;							\
 									\
 	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
+									\
+	head = this_cpu_ptr(event_call->perf_events);			\
+	if (__builtin_constant_p(!__task) && !__task &&			\
+				hlist_empty(head))			\
+		return;							\
+									\
 	__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
 			     sizeof(u64));				\
 	__entry_size -= sizeof(u32);					\
@@ -681,7 +687,6 @@ perf_trace_##call(void *__data, proto)					\
 									\
 	{ assign; }							\
 									\
-	head = this_cpu_ptr(event_call->perf_events);			\
 	perf_trace_buf_submit(entry, __entry_size, rctx, __addr,	\
 		__count, &__regs, head, __task);			\
 }
-- 
1.5.5.1