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Date: Thu, 26 Feb 2009 10:11:05 -0500
From: Jason Baron <jbaron@...hat.com>
To: Mathieu Desnoyers <compudj@...stal.dyndns.org>, mingo@...e.hu
Cc: Masami Hiramatsu <mhiramat@...hat.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Peter Zijlstra <peterz@...radead.org>,
"Frank Ch. Eigler" <fche@...hat.com>, mingo@...e.hu,
rostedt@...dmis.org, linux-kernel@...r.kernel.org,
acme@...stprotocols.net, fweisbec@...il.com
Subject: Re: [PATCH] new irq tracer
On Wed, Feb 25, 2009 at 12:34:12PM -0500, Mathieu Desnoyers wrote:
> * Jason Baron (jbaron@...hat.com) wrote:
> > On Wed, Feb 25, 2009 at 11:48:28AM -0500, Masami Hiramatsu wrote:
> > > KOSAKI Motohiro wrote:
> > > >> /**
> > > >> * handle_IRQ_event - irq action chain handler
> > > >> * @irq: the interrupt number
> > > >> @@ -354,7 +358,9 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
> > > >> local_irq_enable_in_hardirq();
> > > >>
> > > >> do {
> > > >> + trace_irq_entry(irq);
> > > >> ret = action->handler(irq, action->dev_id);
> > > >> + trace_irq_exit(irq, ret);
> > > >> if (ret == IRQ_HANDLED)
> > > >> status |= action->flags;
> > > >> retval |= ret;
> > > >
> > > > Nobdy want unnecessary redundant tracepoint.
> > > > Please discuss with mathieu, and merge his tracepoint.
> > >
> > > Hmm, from the viewpoint of trouble shooting, the place of LTTng's tracepoint
> > > is enough. However, from the same viewpoint, it should pass irq-number
> > > to irq-exit event too, because we may lost some previous events by buffer-overflow
> > > etc.
> > >
> > > trace_irq_entry(irq, NULL);
> > > ret = _handle_IRQ_event(irq, action);
> > > trace_irq_exit(irq, ret);
> > > ^^^^
> > >
> >
> > the lttng tracepoints wrap the calls to _handle_IRQ_event in 3
> > different places. So the above suggested irq tracepoint provides the
> > same information with 4 less tracepoints in the code. So I believe its
> > simpler - plus we can understand which action handlers are handling the
> > interrupt.
> >
>
> The main thing I dislike about only tracing action->handler() calls is
> that you are not tracing an IRQ per se, but rather the invocation of a
> given handler within the interrupt. For instance, it would be difficult
> to calculate the maximum interrupt latency for a given interrupt line,
> because you don't have the "real" irq entry/exit events, just the
> individual handler() calls.
>
> But I agree that knowing which handler is called is important.
>
> How about this compromise :
>
> trace_irq_entry(irq, action)
> _handle_IRQ_event()
> for each action {
> trace_irq_handler(action, ret);
> ret = action->handler(irq, action->dev_id);
> ...
> }
> trace_irq_exit(action_ret);
>
> Would that give you the information you need ?
>
> Here trace_irq_handler would be passed the _current_ action invoked and
> the _previous_ action return value. Note that we should initialize
> irqreturn_t ret to some initial value if we do this. That should keep
> the tracing overhead minimal.
>
maybe...although that would require re-arranging the 'while' loop in
'handle_IRQ_event' from a do..while loop to a 'while' loop, which will
require an extra branch check, and then we still have to record the last 'ret'
value. I'm not that keen on re-arranging this for trace data...
Using Steve's new 'DEFINE_TRACE_FMT', I can get function graph trace
as follows using the original two tracepoints (patch below):
3) | handle_IRQ_event() {
3) | /* (irq_handler_entry) irq=28 handler=eth0 */
3) | e1000_intr_msi() {
3) 2.460 us | __napi_schedule();
3) 9.416 us | }
3) | /* (irq_handler_exit) irq=28 handler=eth0 return=handled */
3) + 22.935 us | }
thanks,
-Jason
Signed-off-by: Jason Baron <jbaron@...hat.com>
---
include/trace/irq.h | 9 +++++++++
include/trace/irq_event_types.h | 17 +++++++++++++++++
kernel/irq/handle.c | 6 ++++++
kernel/trace/events.c | 2 ++
4 files changed, 34 insertions(+), 0 deletions(-)
create mode 100644 include/trace/irq.h
create mode 100644 include/trace/irq_event_types.h
diff --git a/include/trace/irq.h b/include/trace/irq.h
new file mode 100644
index 0000000..ff5d449
--- /dev/null
+++ b/include/trace/irq.h
@@ -0,0 +1,9 @@
+#ifndef _TRACE_IRQ_H
+#define _TRACE_IRQ_H
+
+#include <linux/interrupt.h>
+#include <linux/tracepoint.h>
+
+#include <trace/irq_event_types.h>
+
+#endif
diff --git a/include/trace/irq_event_types.h b/include/trace/irq_event_types.h
new file mode 100644
index 0000000..5889bfd
--- /dev/null
+++ b/include/trace/irq_event_types.h
@@ -0,0 +1,17 @@
+
+/* use <trace/irq.h> instead */
+#ifndef DEFINE_TRACE_FMT
+# error Do not include this file directly.
+# error Unless you know what you are doing.
+#endif
+
+DEFINE_TRACE_FMT(irq_handler_entry,
+ TPPROTO(int irq, struct irqaction *action),
+ TPARGS(irq, action),
+ TPFMT("irq=%d handler=%s", irq, action->name));
+
+DEFINE_TRACE_FMT(irq_handler_exit,
+ TPPROTO(int irq, struct irqaction *action, int ret),
+ TPARGS(irq, action, ret),
+ TPFMT("irq=%d handler=%s return=%s",
+ irq, action->name, ret ? "handled" : "unhandled"));
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index fdff380..bcebc2e 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -18,6 +18,7 @@
#include <linux/rculist.h>
#include <linux/hash.h>
#include <linux/bootmem.h>
+#include <trace/irq.h>
#include "internals.h"
@@ -338,6 +339,9 @@ irqreturn_t no_action(int cpl, void *dev_id)
return IRQ_NONE;
}
+DEFINE_TRACE(irq_handler_entry);
+DEFINE_TRACE(irq_handler_exit);
+
/**
* handle_IRQ_event - irq action chain handler
* @irq: the interrupt number
@@ -354,7 +358,9 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
local_irq_enable_in_hardirq();
do {
+ trace_irq_handler_entry(irq, action);
ret = action->handler(irq, action->dev_id);
+ trace_irq_handler_exit(irq, action, ret);
if (ret == IRQ_HANDLED)
status |= action->flags;
retval |= ret;
diff --git a/kernel/trace/events.c b/kernel/trace/events.c
index 38c89ee..3c75623 100644
--- a/kernel/trace/events.c
+++ b/kernel/trace/events.c
@@ -6,8 +6,10 @@
/* trace/<type>.h here */
#include <trace/sched.h>
+#include <trace/irq.h>
#include "trace_events.h"
/* trace/<type>_event_types.h here */
#include <trace/sched_event_types.h>
+#include <trace/irq_event_types.h>
--
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