linux-kernel - [PATCH 0/8] latched RB-trees and __module

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Date:	Wed, 18 Mar 2015 14:36:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	mingo@...nel.org, rusty@...tcorp.com.au,
	mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	rostedt@...dmis.org, tglx@...utronix.de, peterz@...radead.org
Subject: [PATCH 0/8] latched RB-trees and __module_address()

This series is aimed at making __module_address() go fast(er).

On the way there is:
 - annotates and sanitizes module locking
 - introduces the latched RB-tree
 - employs it to make __module_address() go fast.

I've build and boot tested this on x86_64 with modules and lockdep
enabled.  Performance numbers (below) are done with lockdep disabled.

As mentioned in the previous posting; the reason for writing the latched
RB-tree as generic code is mostly for clarity/documentation purposes; as
there are a number of separate and non trivial bits to the complete
solution.

As measued on my ivb-ep system with 84 modules loaded; prior to patching
the test module (below) reports:

          avg +- stdev
Before:  1689 +- 287 [ns] per __module_address() call
After:    137 +-  38 [ns] per __module_address() call

Note; I have also tested things like: perf record -a -g modprobe
mod_test, to make 'sure' to hit some of the more interesting paths.

---
 kernel/Makefile   |    2 ++
 kernel/mod_test.c |   30 ++++++++++++++++++++++++++++++
 kernel/module.c   |    3 ++-
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/kernel/Makefile b/kernel/Makefile
index 1408b33..ec69606 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -28,6 +28,8 @@ obj-y += irq/
 obj-y += rcu/
 obj-y += livepatch/
 
+obj-m += mod_test.o
+
 obj-$(CONFIG_CHECKPOINT_RESTORE) += kcmp.o
 obj-$(CONFIG_FREEZER) += freezer.o
 obj-$(CONFIG_PROFILING) += profile.o
diff --git a/kernel/mod_test.c b/kernel/mod_test.c
index e69de29..cf32cfc 100644
--- a/kernel/mod_test.c
+++ b/kernel/mod_test.c
@@ -0,0 +1,30 @@
+
+#include <linux/module.h>
+#include <linux/sched.h>
+
+MODULE_LICENSE("GPL");
+
+extern unsigned long module_addr_max;
+
+static int __init test_init(void)
+{
+	u64 t1, t2;
+
+	local_irq_disable();
+	t1 = sched_clock();
+	barrier();
+	t1 = sched_clock() - t1;
+
+	barrier();
+
+	t2 = sched_clock();
+	(void)__module_address(module_addr_max);
+	t2 = sched_clock() - t2;
+	local_irq_enable();
+
+	printk("time: %Lu %Lu %Lu\n", t2 - t1, t1, t2);
+
+	return -EINVAL;
+}
+
+module_init(test_init);
diff --git a/kernel/module.c b/kernel/module.c
index b3d634e..6423dc2 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -155,7 +155,8 @@ static BLOCKING_NOTIFIER_HEAD(module_notify_list);
 
 /* Bounds of module allocation, for speeding __module_address.
  * Protected by module_mutex. */
-static unsigned long module_addr_min = -1UL, module_addr_max = 0;
+unsigned long module_addr_min = -1UL, module_addr_max = 0;
+EXPORT_SYMBOL(module_addr_max);
 
 int register_module_notifier(struct notifier_block *nb)
 {

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