* [PATCH] tracing/ftrace: add missing wake-up on some callsites
@ 2009-02-22 21:56 Frederic Weisbecker
2009-02-22 22:16 ` Ingo Molnar
2009-02-23 15:37 ` Steven Rostedt
0 siblings, 2 replies; 14+ messages in thread
From: Frederic Weisbecker @ 2009-02-22 21:56 UTC (permalink / raw)
To: Ingo Molnar; +Cc: linux-kernel, Steven Rostedt, Arnaldo Carvalho de Melo
Impact: fix unwaken pipe
Now that we use a common wakeup infrastructure, we must append a wakeup
on few callsites which lack it or tasks reading trace_pipe will not be
awaken when events come on few tracers.
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/trace/trace.c | 2 ++
kernel/trace/trace_branch.c | 2 ++
kernel/trace/trace_hw_branches.c | 2 ++
3 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e1f3b99..7f450b6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
out:
preempt_enable_notrace();
+ trace_wake_up();
+
return len;
}
EXPORT_SYMBOL_GPL(trace_vprintk);
diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index c2e68d4..8c8f8c0 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
out:
atomic_dec(&tr->data[cpu]->disabled);
local_irq_restore(flags);
+
+ trace_wake_up();
}
static inline
diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
index 3561aac..ddd87fd 100644
--- a/kernel/trace/trace_hw_branches.c
+++ b/kernel/trace/trace_hw_branches.c
@@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
out:
atomic_dec(&tr->data[cpu]->disabled);
local_irq_restore(irq1);
+
+ trace_wake_up();
}
static void trace_bts_at(const struct bts_trace *trace, void *at)
--
1.6.1
^ permalink raw reply related [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-22 21:56 [PATCH] tracing/ftrace: add missing wake-up on some callsites Frederic Weisbecker
@ 2009-02-22 22:16 ` Ingo Molnar
2009-02-23 15:37 ` Steven Rostedt
1 sibling, 0 replies; 14+ messages in thread
From: Ingo Molnar @ 2009-02-22 22:16 UTC (permalink / raw)
To: Frederic Weisbecker
Cc: linux-kernel, Steven Rostedt, Arnaldo Carvalho de Melo
* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> Impact: fix unwaken pipe
>
> Now that we use a common wakeup infrastructure, we must append a wakeup
> on few callsites which lack it or tasks reading trace_pipe will not be
> awaken when events come on few tracers.
>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> ---
> kernel/trace/trace.c | 2 ++
> kernel/trace/trace_branch.c | 2 ++
> kernel/trace/trace_hw_branches.c | 2 ++
> 3 files changed, 6 insertions(+), 0 deletions(-)
Applied to tip:tracing/ftrace, thanks Frederic!
Ingo
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-22 21:56 [PATCH] tracing/ftrace: add missing wake-up on some callsites Frederic Weisbecker
2009-02-22 22:16 ` Ingo Molnar
@ 2009-02-23 15:37 ` Steven Rostedt
2009-02-23 15:42 ` Steven Rostedt
2009-02-23 16:22 ` Frederic Weisbecker
1 sibling, 2 replies; 14+ messages in thread
From: Steven Rostedt @ 2009-02-23 15:37 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
> Impact: fix unwaken pipe
>
> Now that we use a common wakeup infrastructure, we must append a wakeup
> on few callsites which lack it or tasks reading trace_pipe will not be
> awaken when events come on few tracers.
>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> ---
> kernel/trace/trace.c | 2 ++
> kernel/trace/trace_branch.c | 2 ++
> kernel/trace/trace_hw_branches.c | 2 ++
> 3 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index e1f3b99..7f450b6 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> out:
> preempt_enable_notrace();
>
> + trace_wake_up();
> +
> return len;
> }
> EXPORT_SYMBOL_GPL(trace_vprintk);
> diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> index c2e68d4..8c8f8c0 100644
> --- a/kernel/trace/trace_branch.c
> +++ b/kernel/trace/trace_branch.c
> @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> out:
> atomic_dec(&tr->data[cpu]->disabled);
> local_irq_restore(flags);
> +
> + trace_wake_up();
> }
>
> static inline
> diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> index 3561aac..ddd87fd 100644
> --- a/kernel/trace/trace_hw_branches.c
> +++ b/kernel/trace/trace_hw_branches.c
> @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> out:
> atomic_dec(&tr->data[cpu]->disabled);
> local_irq_restore(irq1);
> +
> + trace_wake_up();
> }
>
> static void trace_bts_at(const struct bts_trace *trace, void *at)
Ah, we don't wake up purposely on these three places. ftrace_printk is
meant to be called anywhere (including the scheduler). And the branch
tracers are also allowed to be called anywhere (they usually are).
Calling "wake_up" from any of these can easily cause a dead lock with the
run queue lock, because all three can be called from with in the
scheduler.
Sorry, but I have to NACK this change.
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 15:37 ` Steven Rostedt
@ 2009-02-23 15:42 ` Steven Rostedt
2009-02-23 16:26 ` Frederic Weisbecker
2009-02-23 16:22 ` Frederic Weisbecker
1 sibling, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2009-02-23 15:42 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, 23 Feb 2009, Steven Rostedt wrote:
>
>
> On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
>
> > Impact: fix unwaken pipe
> >
> > Now that we use a common wakeup infrastructure, we must append a wakeup
> > on few callsites which lack it or tasks reading trace_pipe will not be
> > awaken when events come on few tracers.
> >
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > ---
> > kernel/trace/trace.c | 2 ++
> > kernel/trace/trace_branch.c | 2 ++
> > kernel/trace/trace_hw_branches.c | 2 ++
> > 3 files changed, 6 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index e1f3b99..7f450b6 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> > out:
> > preempt_enable_notrace();
> >
> > + trace_wake_up();
> > +
> > return len;
> > }
> > EXPORT_SYMBOL_GPL(trace_vprintk);
> > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > index c2e68d4..8c8f8c0 100644
> > --- a/kernel/trace/trace_branch.c
> > +++ b/kernel/trace/trace_branch.c
> > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> > out:
> > atomic_dec(&tr->data[cpu]->disabled);
> > local_irq_restore(flags);
> > +
> > + trace_wake_up();
> > }
> >
> > static inline
> > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > index 3561aac..ddd87fd 100644
> > --- a/kernel/trace/trace_hw_branches.c
> > +++ b/kernel/trace/trace_hw_branches.c
> > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> > out:
> > atomic_dec(&tr->data[cpu]->disabled);
> > local_irq_restore(irq1);
> > +
> > + trace_wake_up();
> > }
> >
> > static void trace_bts_at(const struct bts_trace *trace, void *at)
>
> Ah, we don't wake up purposely on these three places. ftrace_printk is
> meant to be called anywhere (including the scheduler). And the branch
> tracers are also allowed to be called anywhere (they usually are).
>
> Calling "wake_up" from any of these can easily cause a dead lock with the
> run queue lock, because all three can be called from with in the
> scheduler.
>
> Sorry, but I have to NACK this change.
Perhaps we could add these callsites back, but we would need to update
trace_wake_up.
Have trace_wake_up set a flag instead, and add a tracepoint around the
scheduler (outside the grabbing of runqueue locks), that will have a
callback to the tracing code. That call back can perform the wakeups.
How does that sound?
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 15:37 ` Steven Rostedt
2009-02-23 15:42 ` Steven Rostedt
@ 2009-02-23 16:22 ` Frederic Weisbecker
1 sibling, 0 replies; 14+ messages in thread
From: Frederic Weisbecker @ 2009-02-23 16:22 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, Feb 23, 2009 at 10:37:52AM -0500, Steven Rostedt wrote:
>
>
> On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
>
> > Impact: fix unwaken pipe
> >
> > Now that we use a common wakeup infrastructure, we must append a wakeup
> > on few callsites which lack it or tasks reading trace_pipe will not be
> > awaken when events come on few tracers.
> >
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > ---
> > kernel/trace/trace.c | 2 ++
> > kernel/trace/trace_branch.c | 2 ++
> > kernel/trace/trace_hw_branches.c | 2 ++
> > 3 files changed, 6 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index e1f3b99..7f450b6 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> > out:
> > preempt_enable_notrace();
> >
> > + trace_wake_up();
> > +
> > return len;
> > }
> > EXPORT_SYMBOL_GPL(trace_vprintk);
> > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > index c2e68d4..8c8f8c0 100644
> > --- a/kernel/trace/trace_branch.c
> > +++ b/kernel/trace/trace_branch.c
> > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> > out:
> > atomic_dec(&tr->data[cpu]->disabled);
> > local_irq_restore(flags);
> > +
> > + trace_wake_up();
> > }
> >
> > static inline
> > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > index 3561aac..ddd87fd 100644
> > --- a/kernel/trace/trace_hw_branches.c
> > +++ b/kernel/trace/trace_hw_branches.c
> > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> > out:
> > atomic_dec(&tr->data[cpu]->disabled);
> > local_irq_restore(irq1);
> > +
> > + trace_wake_up();
> > }
> >
> > static void trace_bts_at(const struct bts_trace *trace, void *at)
>
> Ah, we don't wake up purposely on these three places. ftrace_printk is
> meant to be called anywhere (including the scheduler). And the branch
> tracers are also allowed to be called anywhere (they usually are).
>
> Calling "wake_up" from any of these can easily cause a dead lock with the
> run queue lock, because all three can be called from with in the
> scheduler.
>
> Sorry, but I have to NACK this change.
And fortunately you NACK, I didn't realized how dangerous it can be.
I will send a patch to make these branch tracers use the old polling wake up.
But another solution should be found for ftrace_printk() since it doesn't necessarily
rely on any tracer.
> -- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 15:42 ` Steven Rostedt
@ 2009-02-23 16:26 ` Frederic Weisbecker
2009-02-23 16:51 ` Steven Rostedt
0 siblings, 1 reply; 14+ messages in thread
From: Frederic Weisbecker @ 2009-02-23 16:26 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, Feb 23, 2009 at 10:42:04AM -0500, Steven Rostedt wrote:
>
> On Mon, 23 Feb 2009, Steven Rostedt wrote:
>
> >
> >
> > On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
> >
> > > Impact: fix unwaken pipe
> > >
> > > Now that we use a common wakeup infrastructure, we must append a wakeup
> > > on few callsites which lack it or tasks reading trace_pipe will not be
> > > awaken when events come on few tracers.
> > >
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > > ---
> > > kernel/trace/trace.c | 2 ++
> > > kernel/trace/trace_branch.c | 2 ++
> > > kernel/trace/trace_hw_branches.c | 2 ++
> > > 3 files changed, 6 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > > index e1f3b99..7f450b6 100644
> > > --- a/kernel/trace/trace.c
> > > +++ b/kernel/trace/trace.c
> > > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> > > out:
> > > preempt_enable_notrace();
> > >
> > > + trace_wake_up();
> > > +
> > > return len;
> > > }
> > > EXPORT_SYMBOL_GPL(trace_vprintk);
> > > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > > index c2e68d4..8c8f8c0 100644
> > > --- a/kernel/trace/trace_branch.c
> > > +++ b/kernel/trace/trace_branch.c
> > > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> > > out:
> > > atomic_dec(&tr->data[cpu]->disabled);
> > > local_irq_restore(flags);
> > > +
> > > + trace_wake_up();
> > > }
> > >
> > > static inline
> > > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > > index 3561aac..ddd87fd 100644
> > > --- a/kernel/trace/trace_hw_branches.c
> > > +++ b/kernel/trace/trace_hw_branches.c
> > > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> > > out:
> > > atomic_dec(&tr->data[cpu]->disabled);
> > > local_irq_restore(irq1);
> > > +
> > > + trace_wake_up();
> > > }
> > >
> > > static void trace_bts_at(const struct bts_trace *trace, void *at)
> >
> > Ah, we don't wake up purposely on these three places. ftrace_printk is
> > meant to be called anywhere (including the scheduler). And the branch
> > tracers are also allowed to be called anywhere (they usually are).
> >
> > Calling "wake_up" from any of these can easily cause a dead lock with the
> > run queue lock, because all three can be called from with in the
> > scheduler.
> >
> > Sorry, but I have to NACK this change.
>
>
> Perhaps we could add these callsites back, but we would need to update
> trace_wake_up.
>
> Have trace_wake_up set a flag instead, and add a tracepoint around the
> scheduler (outside the grabbing of runqueue locks), that will have a
> callback to the tracing code. That call back can perform the wakeups.
>
> How does that sound?
That sounds good but only for these particular tracers I guess.
> -- Steve
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 16:26 ` Frederic Weisbecker
@ 2009-02-23 16:51 ` Steven Rostedt
2009-02-23 17:05 ` Frederic Weisbecker
0 siblings, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2009-02-23 16:51 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> >
> > Perhaps we could add these callsites back, but we would need to update
> > trace_wake_up.
> >
> > Have trace_wake_up set a flag instead, and add a tracepoint around the
> > scheduler (outside the grabbing of runqueue locks), that will have a
> > callback to the tracing code. That call back can perform the wakeups.
> >
> > How does that sound?
>
>
> That sounds good but only for these particular tracers I guess.
OK, what about making a trace_delay_wake_up()?
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 16:51 ` Steven Rostedt
@ 2009-02-23 17:05 ` Frederic Weisbecker
2009-02-23 17:13 ` Steven Rostedt
0 siblings, 1 reply; 14+ messages in thread
From: Frederic Weisbecker @ 2009-02-23 17:05 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
>
> On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > >
> > > Perhaps we could add these callsites back, but we would need to update
> > > trace_wake_up.
> > >
> > > Have trace_wake_up set a flag instead, and add a tracepoint around the
> > > scheduler (outside the grabbing of runqueue locks), that will have a
> > > callback to the tracing code. That call back can perform the wakeups.
> > >
> > > How does that sound?
> >
> >
> > That sounds good but only for these particular tracers I guess.
>
> OK, what about making a trace_delay_wake_up()?
Which would send a delayed work to wake up?
> -- Steve
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 17:05 ` Frederic Weisbecker
@ 2009-02-23 17:13 ` Steven Rostedt
2009-02-23 17:34 ` Frederic Weisbecker
2009-02-23 17:37 ` Ingo Molnar
0 siblings, 2 replies; 14+ messages in thread
From: Steven Rostedt @ 2009-02-23 17:13 UTC (permalink / raw)
To: Frederic Weisbecker; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
> >
> > On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > > >
> > > > Perhaps we could add these callsites back, but we would need to update
> > > > trace_wake_up.
> > > >
> > > > Have trace_wake_up set a flag instead, and add a tracepoint around the
> > > > scheduler (outside the grabbing of runqueue locks), that will have a
> > > > callback to the tracing code. That call back can perform the wakeups.
> > > >
> > > > How does that sound?
> > >
> > >
> > > That sounds good but only for these particular tracers I guess.
> >
> > OK, what about making a trace_delay_wake_up()?
>
>
> Which would send a delayed work to wake up?
No, I was thinking that trace_delay_wake_up() would be called by these
dangerous call sites. Then a per_cpu flag could be set. We could have a
trace point in the scheduler code that is outside holding a runqueue lock,
and this trace point would call a trace function that will clear the per
cpu flag, and then call trace_wake_up().
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 17:13 ` Steven Rostedt
@ 2009-02-23 17:34 ` Frederic Weisbecker
2009-02-23 17:37 ` Ingo Molnar
1 sibling, 0 replies; 14+ messages in thread
From: Frederic Weisbecker @ 2009-02-23 17:34 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, LKML, Arnaldo Carvalho de Melo
On Mon, Feb 23, 2009 at 12:13:36PM -0500, Steven Rostedt wrote:
>
> On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
>
> > On Mon, Feb 23, 2009 at 11:51:30AM -0500, Steven Rostedt wrote:
> > >
> > > On Mon, 23 Feb 2009, Frederic Weisbecker wrote:
> > > > >
> > > > > Perhaps we could add these callsites back, but we would need to update
> > > > > trace_wake_up.
> > > > >
> > > > > Have trace_wake_up set a flag instead, and add a tracepoint around the
> > > > > scheduler (outside the grabbing of runqueue locks), that will have a
> > > > > callback to the tracing code. That call back can perform the wakeups.
> > > > >
> > > > > How does that sound?
> > > >
> > > >
> > > > That sounds good but only for these particular tracers I guess.
> > >
> > > OK, what about making a trace_delay_wake_up()?
> >
> >
> > Which would send a delayed work to wake up?
>
> No, I was thinking that trace_delay_wake_up() would be called by these
> dangerous call sites. Then a per_cpu flag could be set. We could have a
> trace point in the scheduler code that is outside holding a runqueue lock,
> and this trace point would call a trace function that will clear the per
> cpu flag, and then call trace_wake_up().
>
Oh yes, sounds nice!
> -- Steve
>
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 17:13 ` Steven Rostedt
2009-02-23 17:34 ` Frederic Weisbecker
@ 2009-02-23 17:37 ` Ingo Molnar
2009-02-23 18:03 ` Steven Rostedt
1 sibling, 1 reply; 14+ messages in thread
From: Ingo Molnar @ 2009-02-23 17:37 UTC (permalink / raw)
To: Steven Rostedt, Peter Zijlstra
Cc: Frederic Weisbecker, LKML, Arnaldo Carvalho de Melo
* Steven Rostedt <rostedt@goodmis.org> wrote:
> > Which would send a delayed work to wake up?
>
> No, I was thinking that trace_delay_wake_up() would be called
> by these dangerous call sites. Then a per_cpu flag could be
> set. We could have a trace point in the scheduler code that is
> outside holding a runqueue lock, and this trace point would
> call a trace function that will clear the per cpu flag, and
> then call trace_wake_up().
No, that's very roundabout and ugly. If we putting a tracepoint
there we might as well put real scheduler code there that looks
for such a flag. But i'm not convinced we need a flag ...
Ingo
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 17:37 ` Ingo Molnar
@ 2009-02-23 18:03 ` Steven Rostedt
2009-02-23 18:09 ` Ingo Molnar
2009-02-27 17:04 ` Masami Hiramatsu
0 siblings, 2 replies; 14+ messages in thread
From: Steven Rostedt @ 2009-02-23 18:03 UTC (permalink / raw)
To: Ingo Molnar
Cc: Peter Zijlstra, Frederic Weisbecker, LKML, Arnaldo Carvalho de Melo
On Mon, 23 Feb 2009, Ingo Molnar wrote:
>
> * Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > > Which would send a delayed work to wake up?
> >
> > No, I was thinking that trace_delay_wake_up() would be called
> > by these dangerous call sites. Then a per_cpu flag could be
> > set. We could have a trace point in the scheduler code that is
> > outside holding a runqueue lock, and this trace point would
> > call a trace function that will clear the per cpu flag, and
> > then call trace_wake_up().
>
> No, that's very roundabout and ugly. If we putting a tracepoint
> there we might as well put real scheduler code there that looks
> for such a flag. But i'm not convinced we need a flag ...
Just a suggestion. I was trying to keep the tracer from being an overhead.
But what else would you suggest? Just having the scheduler call
trace_wakeup?
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 18:03 ` Steven Rostedt
@ 2009-02-23 18:09 ` Ingo Molnar
2009-02-27 17:04 ` Masami Hiramatsu
1 sibling, 0 replies; 14+ messages in thread
From: Ingo Molnar @ 2009-02-23 18:09 UTC (permalink / raw)
To: Steven Rostedt
Cc: Peter Zijlstra, Frederic Weisbecker, LKML, Arnaldo Carvalho de Melo
* Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 23 Feb 2009, Ingo Molnar wrote:
>
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > > Which would send a delayed work to wake up?
> > >
> > > No, I was thinking that trace_delay_wake_up() would be
> > > called by these dangerous call sites. Then a per_cpu flag
> > > could be set. We could have a trace point in the scheduler
> > > code that is outside holding a runqueue lock, and this
> > > trace point would call a trace function that will clear
> > > the per cpu flag, and then call trace_wake_up().
> >
> > No, that's very roundabout and ugly. If we putting a
> > tracepoint there we might as well put real scheduler code
> > there that looks for such a flag. But i'm not convinced we
> > need a flag ...
>
> Just a suggestion. I was trying to keep the tracer from being
> an overhead. But what else would you suggest? Just having the
> scheduler call trace_wakeup?
i think we could use a TIF flag to trigger a wakeup at the
return-to-userspace (or return-from-IRQ) stage or so?
Ingo
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites
2009-02-23 18:03 ` Steven Rostedt
2009-02-23 18:09 ` Ingo Molnar
@ 2009-02-27 17:04 ` Masami Hiramatsu
1 sibling, 0 replies; 14+ messages in thread
From: Masami Hiramatsu @ 2009-02-27 17:04 UTC (permalink / raw)
To: Steven Rostedt
Cc: Ingo Molnar, Peter Zijlstra, Frederic Weisbecker, LKML,
Arnaldo Carvalho de Melo, systemtap-ml
Steven Rostedt wrote:
> On Mon, 23 Feb 2009, Ingo Molnar wrote:
>
>> * Steven Rostedt <rostedt@goodmis.org> wrote:
>>
>>>> Which would send a delayed work to wake up?
>>> No, I was thinking that trace_delay_wake_up() would be called
>>> by these dangerous call sites. Then a per_cpu flag could be
>>> set. We could have a trace point in the scheduler code that is
>>> outside holding a runqueue lock, and this trace point would
>>> call a trace function that will clear the per cpu flag, and
>>> then call trace_wake_up().
>> No, that's very roundabout and ugly. If we putting a tracepoint
>> there we might as well put real scheduler code there that looks
>> for such a flag. But i'm not convinced we need a flag ...
>
> Just a suggestion. I was trying to keep the tracer from being an overhead.
> But what else would you suggest? Just having the scheduler call
> trace_wakeup?
Actually, Systemtap(LTTng too?) also has same problem. Currently,
we're using a periodical timer to wake the reader process up.
I assume if we can put a tracepoint at the beginning of schedule(),
we can share it.
Thank you,
>
> -- Steve
>
> --
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> Please read the FAQ at http://www.tux.org/lkml/
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com
^ permalink raw reply [flat|nested] 14+ messages in thread
end of thread, other threads:[~2009-02-27 17:03 UTC | newest]
Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2009-02-22 21:56 [PATCH] tracing/ftrace: add missing wake-up on some callsites Frederic Weisbecker
2009-02-22 22:16 ` Ingo Molnar
2009-02-23 15:37 ` Steven Rostedt
2009-02-23 15:42 ` Steven Rostedt
2009-02-23 16:26 ` Frederic Weisbecker
2009-02-23 16:51 ` Steven Rostedt
2009-02-23 17:05 ` Frederic Weisbecker
2009-02-23 17:13 ` Steven Rostedt
2009-02-23 17:34 ` Frederic Weisbecker
2009-02-23 17:37 ` Ingo Molnar
2009-02-23 18:03 ` Steven Rostedt
2009-02-23 18:09 ` Ingo Molnar
2009-02-27 17:04 ` Masami Hiramatsu
2009-02-23 16:22 ` Frederic Weisbecker
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