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Message-ID: <20080925215611.GA25701@elte.hu>
Date: Thu, 25 Sep 2008 23:56:11 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Martin Bligh <mbligh@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Martin Bligh <mbligh@...igh.org>, linux-kernel@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>,
prasad@...ux.vnet.ibm.com,
Mathieu Desnoyers <compudj@...stal.dyndns.org>,
"Frank Ch. Eigler" <fche@...hat.com>,
David Wilder <dwilder@...ibm.com>, hch@....de,
Tom Zanussi <zanussi@...cast.net>,
Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH 1/3] Unified trace buffer
* Ingo Molnar <mingo@...e.hu> wrote:
> <idle>-0 [001] 52.291807: ktime_get <-tick_nohz_stop_sched_tick
> <idle>-0 [001] 52.291807: ktime_get_ts <-ktime_get
> <idle>-0 [001] 52.291808: getnstimeofday <-ktime_get_ts
> <idle>-0 [001] 52.291808: acpi_pm_read <-getnstimeofday
> <idle>-0 [001] 52.291810: set_normalized_timespec <-ktime_get_ts
> <idle>-0 [001] 52.291811: get_next_timer_interrupt <-tick_nohz_stop_sched_tick
>
> it worked just fine in my first blind attempt.
here is the observations from my second blind attempt - this time to
show that we can trace even lockdep internals just fine.
I applied the patch attached below: it removes all the -pg removals from
kernel/Makefile and restores the notrace markings in kernel/lockdep.c
that commit 1d09daa5 ("ftrace: use Makefile to remove tracing from
lockdep") removed.
then i enabled the whole lockdep machinery (to insert as much extra code
as possible):
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_LOCK_ALLOC=y
CONFIG_PROVE_LOCKING=y
CONFIG_LOCKDEP=y
CONFIG_LOCK_STAT=y
CONFIG_DEBUG_LOCKDEP=y
CONFIG_TRACE_IRQFLAGS=y
and enabled ftrace function tracing:
CONFIG_FTRACE=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_FTRACE_MCOUNT_RECORD=y
[ mcount-record is a new ftrace feature for v2.6.28 ]
and rebuilt and rebooted into the kernel, and enabled ftrace.
It worked just fine this time too, and i was able to trace inside
lockdep and lockstat internals:
<idle>-0 [001] 71.120828: _spin_lock <-tick_do_update_jiffies64
<idle>-0 [001] 71.120829: __lock_acquire <-lock_acquire
<idle>-0 [001] 71.120829: lock_acquired <-_spin_lock
<idle>-0 [001] 71.120829: print_lock_contention_bug <-lock_acquired
<idle>-0 [001] 71.120830: do_timer <-tick_do_update_jiffies64
this wasnt done since May this year (since commit 1d09daa5).
It's absolutely not unrobust. Yes, more code will always regress more
than no code, but it's a cost/benefit balance not a design must-have.
And to prove me wrong i'm sure we'll have some really bad cpu_clock()
regression within the next 24 hours ;)
Why did we do commit 1d09daa5, 6ec56232 and c349e0a0 which marked all
these .o's notrace? Partly to address a real (meanwhile fixed)
regression wrt. sched_clock() [and this supports your point], partly to
remove extra unnecessary trace entries from debug infrastructure, and
partly out of pure paranoia: i didnt want to see _any_ ftrace lockup in
mainline, i wanted it to have the kind of almost perfect track record
that lockdep gathered.
Maybe that was the wrong thing to do as we hide certain trace entries -
we could certainly apply the patch below. Hm?
Ingo
------------->
Index: linux/kernel/Makefile
===================================================================
--- linux.orig/kernel/Makefile
+++ linux/kernel/Makefile
@@ -15,13 +15,11 @@ CFLAGS_REMOVE_sched.o = -mno-spe
ifdef CONFIG_FTRACE
# Do not trace debug files and internal ftrace files
-CFLAGS_REMOVE_lockdep.o = -pg
CFLAGS_REMOVE_lockdep_proc.o = -pg
CFLAGS_REMOVE_mutex-debug.o = -pg
CFLAGS_REMOVE_rtmutex-debug.o = -pg
CFLAGS_REMOVE_cgroup-debug.o = -pg
CFLAGS_REMOVE_sched_clock.o = -pg
-CFLAGS_REMOVE_sched.o = -mno-spe -pg
endif
obj-$(CONFIG_PROFILING) += profile.o
Index: linux/kernel/lockdep.c
===================================================================
--- linux.orig/kernel/lockdep.c
+++ linux/kernel/lockdep.c
@@ -283,14 +283,14 @@ static struct list_head chainhash_table[
((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \
(key2))
-void lockdep_off(void)
+notrace void lockdep_off(void)
{
current->lockdep_recursion++;
}
EXPORT_SYMBOL(lockdep_off);
-void lockdep_on(void)
+notrace void lockdep_on(void)
{
current->lockdep_recursion--;
}
@@ -1136,7 +1136,7 @@ find_usage_forwards(struct lock_class *s
* Return 1 otherwise and keep <backwards_match> unchanged.
* Return 0 on error.
*/
-static noinline int
+static noinline notrace int
find_usage_backwards(struct lock_class *source, unsigned int depth)
{
struct lock_list *entry;
@@ -1748,7 +1748,7 @@ static inline int validate_chain(struct
* We are building curr_chain_key incrementally, so double-check
* it from scratch, to make sure that it's done correctly:
*/
-static void check_chain_key(struct task_struct *curr)
+static notrace void check_chain_key(struct task_struct *curr)
{
#ifdef CONFIG_DEBUG_LOCKDEP
struct held_lock *hlock, *prev_hlock = NULL;
@@ -2122,7 +2122,7 @@ static int mark_lock_irq(struct task_str
/*
* Mark all held locks with a usage bit:
*/
-static int
+static notrace int
mark_held_locks(struct task_struct *curr, int hardirq)
{
enum lock_usage_bit usage_bit;
@@ -2169,7 +2169,7 @@ void early_boot_irqs_on(void)
/*
* Hardirqs will be enabled:
*/
-void trace_hardirqs_on_caller(unsigned long a0)
+void notrace trace_hardirqs_on_caller(unsigned long a0)
{
struct task_struct *curr = current;
unsigned long ip;
@@ -2215,7 +2215,7 @@ void trace_hardirqs_on_caller(unsigned l
}
EXPORT_SYMBOL(trace_hardirqs_on_caller);
-void trace_hardirqs_on(void)
+void notrace trace_hardirqs_on(void)
{
trace_hardirqs_on_caller(CALLER_ADDR0);
}
@@ -2224,7 +2224,7 @@ EXPORT_SYMBOL(trace_hardirqs_on);
/*
* Hardirqs were disabled:
*/
-void trace_hardirqs_off_caller(unsigned long a0)
+void notrace trace_hardirqs_off_caller(unsigned long a0)
{
struct task_struct *curr = current;
@@ -2249,7 +2249,7 @@ void trace_hardirqs_off_caller(unsigned
}
EXPORT_SYMBOL(trace_hardirqs_off_caller);
-void trace_hardirqs_off(void)
+void notrace trace_hardirqs_off(void)
{
trace_hardirqs_off_caller(CALLER_ADDR0);
}
@@ -2415,7 +2415,7 @@ static inline int separate_irq_context(s
/*
* Mark a lock with a usage bit, and validate the state transition:
*/
-static int mark_lock(struct task_struct *curr, struct held_lock *this,
+static notrace int mark_lock(struct task_struct *curr, struct held_lock *this,
enum lock_usage_bit new_bit)
{
unsigned int new_mask = 1 << new_bit, ret = 1;
@@ -2869,7 +2869,7 @@ __lock_release(struct lockdep_map *lock,
/*
* Check whether we follow the irq-flags state precisely:
*/
-static void check_flags(unsigned long flags)
+static notrace void check_flags(unsigned long flags)
{
#if defined(CONFIG_PROVE_LOCKING) && defined(CONFIG_DEBUG_LOCKDEP) && \
defined(CONFIG_TRACE_IRQFLAGS)
@@ -2927,7 +2927,7 @@ EXPORT_SYMBOL_GPL(lock_set_subclass);
* We are not always called with irqs disabled - do that here,
* and also avoid lockdep recursion:
*/
-void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
+notrace void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
int trylock, int read, int check,
struct lockdep_map *nest_lock, unsigned long ip)
{
@@ -2948,7 +2948,7 @@ void lock_acquire(struct lockdep_map *lo
EXPORT_SYMBOL_GPL(lock_acquire);
-void lock_release(struct lockdep_map *lock, int nested,
+notrace void lock_release(struct lockdep_map *lock, int nested,
unsigned long ip)
{
unsigned long flags;
--
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