linux-kernel - Re: [PATCH 05/05] update - Linux Kernel Markers, non optimised architectures

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Date:	Fri, 12 Jan 2007 13:23:01 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Christoph Hellwig <hch@...radead.org>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com,
	Douglas Niehaus <niehaus@...s.ku.edu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 05/05] update - Linux Kernel Markers, non optimised architectures

* Nick Piggin (nickpiggin@...oo.com.au) wrote:
> OK, well one problem is that it can cause a resched event to be lost, so
> you might say it has more side-effects without checking resched.
> 

Here is the patch that implements this. I also did a cosmetic change to
linux/marker.h. Preliminary tests of running the markers with preempt_enable()
with LTTng 0.6.56 instrumentation shows no problem.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>

--- a/include/asm-generic/marker.h
+++ b/include/asm-generic/marker.h
@@ -39,7 +39,7 @@ struct __mark_marker {
 		if (unlikely(__marker_enable_##name)) { \
 			preempt_disable(); \
 			(*__mark_call_##name)(format, ## args); \
-			preempt_enable_no_resched(); \
+			preempt_enable(); \
 		} \
 	} while (0)
 
--- a/include/asm-i386/marker.h
+++ b/include/asm-i386/marker.h
@@ -42,7 +42,7 @@ struct __mark_marker {
 		if (unlikely(condition)) { \
 			preempt_disable(); \
 			(*__mark_call_##name)(format, ## args); \
-			preempt_enable_no_resched(); \
+			preempt_enable(); \
 		} \
 	} while (0)
 
--- a/include/asm-powerpc/marker.h
+++ b/include/asm-powerpc/marker.h
@@ -45,7 +45,7 @@ struct __mark_marker {
 		if (unlikely(condition)) { \
 			preempt_disable(); \
 			(*__mark_call_##name)(format, ## args); \
-			preempt_enable_no_resched(); \
+			preempt_enable(); \
 		} \
 	} while (0)
 
--- a/include/linux/marker.h
+++ b/include/linux/marker.h
@@ -8,12 +8,12 @@
  *
  * Example :
  *
- * MARK(subsystem_event, "%d %s %p[struct task_struct *]",
+ * MARK(subsystem_event, "%d %s %p[struct task_struct]",
  *   someint, somestring, current);
  * Where :
  * - Subsystem is the name of your subsystem.
  * - event is the name of the event to mark.
- * - "%d %s %p[struct task_struct *]" is the formatted string for printk.
+ * - "%d %s %p[struct task_struct]" is the formatted string for printk.
  * - someint is an integer.
  * - somestring is a char pointer.
  * - current is a pointer to a struct task_struct.
@@ -27,6 +27,9 @@
  * Markers can be put in inline functions, inlined static functions and
  * unrolled loops.
  *
+ * Note : It is safe to put markers within preempt-safe code : preempt_enable()
+ * will not call the scheduler due to the tests in preempt_schedule().
+ *
  * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
  *
  * This file is released under the GPLv2.
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