linux-kernel - Re: [PATCH v4 0/2] rcu: uninline rcu_lock_acquire() and rcu_lock

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Message-ID: <20140702153901.GA9535@redhat.com>
Date:	Wed, 2 Jul 2014 17:39:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/2] rcu: uninline rcu_lock_acquire() and
	rcu_lock_release()

On 07/01, Oleg Nesterov wrote:
>
> On 06/30, Paul E. McKenney wrote:
> >
> > On Mon, Jun 30, 2014 at 06:18:37PM +0200, Oleg Nesterov wrote:
> > >
> > > 2/2 is new and hopefully trivial. But! the numbers look suspiciously
> > > good, I do not understand where does the difference come from...
> >
> > Probably from rcu_dereference_raw() and rcu_dereference_check(..., 1).  ;-)
>
> Yes, sure, this was the motivation for the patch. But I didn't expect the
> 50k difference ;)
>
> OK, I understand now. I forgot that every list_for_each_rcu/list_entry_rcu
> has rcu_dereference_raw().

And this naturally suggests that rcu_read_lock_held() should be uninlined
too (and rcu_read_lock_sched_held(), but this needs another patch).

But I still can't understand the difference reported by "size vmlinux",

	- 5541731 3014560 14757888 23314179
	+ 5513182 3026848 14757888 23297918

it removes 28K from .text, but somehow it adds 12K to .data. I do not
see any difference in .data when I compare individual .o files before/
after this patch.

Confused.

Oleg.


diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e8c55d8..8980817 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -378,42 +378,8 @@ extern void rcu_lock_release_bh(void);
 extern void rcu_lock_acquire_sched(void);
 extern void rcu_lock_release_sched(void);
 
-/**
- * rcu_read_lock_held() - might we be in RCU read-side critical section?
- *
- * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
- * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
- * this assumes we are in an RCU read-side critical section unless it can
- * prove otherwise.  This is useful for debug checks in functions that
- * require that they be called within an RCU read-side critical section.
- *
- * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
- * and while lockdep is disabled.
- *
- * Note that rcu_read_lock() and the matching rcu_read_unlock() must
- * occur in the same context, for example, it is illegal to invoke
- * rcu_read_unlock() in process context if the matching rcu_read_lock()
- * was invoked from within an irq handler.
- *
- * Note that rcu_read_lock() is disallowed if the CPU is either idle or
- * offline from an RCU perspective, so check for those as well.
- */
-static inline int rcu_read_lock_held(void)
-{
-	if (!debug_lockdep_rcu_enabled())
-		return 1;
-	if (!rcu_is_watching())
-		return 0;
-	if (!rcu_lockdep_current_cpu_online())
-		return 0;
-	return lock_is_held(&rcu_lock_map);
-}
-
-/*
- * rcu_read_lock_bh_held() is defined out of line to avoid #include-file
- * hell.
- */
-int rcu_read_lock_bh_held(void);
+extern int rcu_read_lock_held(void);
+extern int rcu_read_lock_bh_held(void);
 
 /**
  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c2209eb..ea4af81 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -137,6 +137,38 @@ int notrace debug_lockdep_rcu_enabled(void)
 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 
 /**
+ * rcu_read_lock_held() - might we be in RCU read-side critical section?
+ *
+ * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
+ * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
+ * this assumes we are in an RCU read-side critical section unless it can
+ * prove otherwise.  This is useful for debug checks in functions that
+ * require that they be called within an RCU read-side critical section.
+ *
+ * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
+ * and while lockdep is disabled.
+ *
+ * Note that rcu_read_lock() and the matching rcu_read_unlock() must
+ * occur in the same context, for example, it is illegal to invoke
+ * rcu_read_unlock() in process context if the matching rcu_read_lock()
+ * was invoked from within an irq handler.
+ *
+ * Note that rcu_read_lock() is disallowed if the CPU is either idle or
+ * offline from an RCU perspective, so check for those as well.
+ */
+int rcu_read_lock_held(void)
+{
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
+	return lock_is_held(&rcu_lock_map);
+}
+EXPORT_SYMBOL_GPL(rcu_read_lock_held);
+
+/**
  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
  *
  * Check for bottom half being disabled, which covers both the

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