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From: Byungchul Park <byungchul.park@lge.com>
To: peterz@infradead.org, mingo@kernel.org
Cc: tglx@linutronix.de, walken@google.com, boqun.feng@gmail.com,
	kirill@shutemov.name, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, iamjoonsoo.kim@lge.com,
	akpm@linux-foundation.org, npiggin@gmail.com
Subject: [PATCH v3 02/15] x86/dumpstack: Add save_stack_trace()_fast()
Date: Tue, 13 Sep 2016 18:45:01 +0900	[thread overview]
Message-ID: <1473759914-17003-3-git-send-email-byungchul.park@lge.com> (raw)
In-Reply-To: <1473759914-17003-1-git-send-email-byungchul.park@lge.com>

In non-oops case, it's usually not necessary to check all words of stack
area to extract backtrace. Instead, we can achieve it by tracking frame
pointer. So made it possible to save stack trace lightly in normal case.

I measured its ovehead and printed its difference of sched_clock() with
my QEMU x86 machine. The latency was improved over 80% when
trace->max_entries = 5.

Before this patch:

[    2.795000] save_stack_trace() takes 21147 ns
[    2.795397] save_stack_trace() takes 20230 ns
[    2.795397] save_stack_trace() takes 31274 ns
[    2.795739] save_stack_trace() takes 19706 ns
[    2.796484] save_stack_trace() takes 20266 ns
[    2.796484] save_stack_trace() takes 20902 ns
[    2.797000] save_stack_trace() takes 38110 ns
[    2.797510] save_stack_trace() takes 20224 ns
[    2.798181] save_stack_trace() takes 20172 ns
[    2.798837] save_stack_trace() takes 20824 ns

After this patch:

[    3.133807] save_stack_trace() takes 3297 ns
[    3.133954] save_stack_trace() takes 3330 ns
[    3.134235] save_stack_trace() takes 3517 ns
[    3.134711] save_stack_trace() takes 3773 ns
[    3.135000] save_stack_trace() takes 3685 ns
[    3.135541] save_stack_trace() takes 4757 ns
[    3.135865] save_stack_trace() takes 3420 ns
[    3.136000] save_stack_trace() takes 3329 ns
[    3.137000] save_stack_trace() takes 4058 ns
[    3.137000] save_stack_trace() takes 3499 ns

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 arch/x86/kernel/stacktrace.c | 25 +++++++++++++++++++++++++
 include/linux/stacktrace.h   |  2 ++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index a44de4d..d8da90f 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -53,6 +53,10 @@ static int save_stack_end(void *data)
 	return trace->nr_entries >= trace->max_entries;
 }
 
+/*
+ * This operation should be used in the oops case where
+ * stack might be broken.
+ */
 static const struct stacktrace_ops save_stack_ops = {
 	.stack		= save_stack_stack,
 	.address	= save_stack_address,
@@ -60,6 +64,13 @@ static const struct stacktrace_ops save_stack_ops = {
 	.end_walk	= save_stack_end,
 };
 
+static const struct stacktrace_ops save_stack_ops_fast = {
+	.stack		= save_stack_stack,
+	.address	= save_stack_address,
+	.walk_stack	= print_context_stack_bp,
+	.end_walk	= save_stack_end,
+};
+
 static const struct stacktrace_ops save_stack_ops_nosched = {
 	.stack		= save_stack_stack,
 	.address	= save_stack_address_nosched,
@@ -68,6 +79,7 @@ static const struct stacktrace_ops save_stack_ops_nosched = {
 
 /*
  * Save stack-backtrace addresses into a stack_trace buffer.
+ * It works even in oops.
  */
 void save_stack_trace(struct stack_trace *trace)
 {
@@ -77,6 +89,19 @@ void save_stack_trace(struct stack_trace *trace)
 }
 EXPORT_SYMBOL_GPL(save_stack_trace);
 
+/*
+ * Save stack-backtrace addresses into a stack_trace buffer.
+ * This is perfered in normal case where we expect the stack is
+ * reliable.
+ */
+void save_stack_trace_fast(struct stack_trace *trace)
+{
+	dump_trace(current, NULL, NULL, 0, &save_stack_ops_fast, trace);
+	if (trace->nr_entries < trace->max_entries)
+		trace->entries[trace->nr_entries++] = ULONG_MAX;
+}
+EXPORT_SYMBOL_GPL(save_stack_trace_fast);
+
 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 {
 	dump_trace(current, regs, NULL, 0, &save_stack_ops, trace);
diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
index 0a34489..ddef1d0 100644
--- a/include/linux/stacktrace.h
+++ b/include/linux/stacktrace.h
@@ -14,6 +14,7 @@ struct stack_trace {
 };
 
 extern void save_stack_trace(struct stack_trace *trace);
+extern void save_stack_trace_fast(struct stack_trace *trace);
 extern void save_stack_trace_regs(struct pt_regs *regs,
 				  struct stack_trace *trace);
 extern void save_stack_trace_tsk(struct task_struct *tsk,
@@ -31,6 +32,7 @@ extern void save_stack_trace_user(struct stack_trace *trace);
 
 #else
 # define save_stack_trace(trace)			do { } while (0)
+# define save_stack_trace_fast(trace)			do { } while (0)
 # define save_stack_trace_tsk(tsk, trace)		do { } while (0)
 # define save_stack_trace_user(trace)			do { } while (0)
 # define print_stack_trace(trace, spaces)		do { } while (0)
-- 
1.9.1

  parent reply	other threads:[~2016-09-13  9:49 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-13  9:44 [PATCH v3 00/15] lockdep: Implement crossrelease feature Byungchul Park
2016-09-13  9:45 ` [PATCH v3 01/15] x86/dumpstack: Optimize save_stack_trace Byungchul Park
2016-09-13 13:18   ` Josh Poimboeuf
2016-09-13 14:54     ` Byungchul Park
2016-09-13  9:45 ` Byungchul Park [this message]
2016-09-13 13:20   ` [PATCH v3 02/15] x86/dumpstack: Add save_stack_trace()_fast() Josh Poimboeuf
2016-09-13  9:45 ` [PATCH v3 03/15] lockdep: Refactor lookup_chain_cache() Byungchul Park
2016-09-15 15:33   ` Nilay Vaish
2016-09-19  3:05     ` Byungchul Park
2016-09-19 16:36       ` Nilay Vaish
2016-09-20  2:00         ` Byungchul Park
2016-09-13  9:45 ` [PATCH v3 04/15] lockdep: Add a function building a chain between two classes Byungchul Park
2016-09-13  9:45 ` [PATCH v3 05/15] lockdep: Make check_prev_add can use a separate stack_trace Byungchul Park
2016-09-13  9:45 ` [PATCH v3 06/15] lockdep: Make save_trace can skip stack tracing of the current Byungchul Park
2016-09-13  9:45 ` [PATCH v3 07/15] lockdep: Implement crossrelease feature Byungchul Park
2016-09-13 10:05   ` Peter Zijlstra
2016-09-13 12:09     ` Peter Zijlstra
2016-09-13 15:14     ` Byungchul Park
2016-09-13 15:05   ` Peter Zijlstra
2016-09-13 17:12     ` Byungchul Park
2016-09-13 19:38       ` Peter Zijlstra
2016-09-13 21:42         ` Peter Zijlstra
2016-09-14  1:01           ` Byungchul Park
2016-09-14  2:27         ` Byungchul Park
2016-09-14  4:49           ` Byungchul Park
2016-09-14  8:11           ` Peter Zijlstra
2016-09-19  2:41             ` Byungchul Park
2016-09-19  8:50               ` Peter Zijlstra
2016-09-20  5:50                 ` Byungchul Park
2016-09-20  6:26                   ` Byungchul Park
2016-09-21  1:37                   ` Byungchul Park
2016-09-22  2:57                 ` Byungchul Park
2016-09-13  9:45 ` [PATCH v3 08/15] lockdep: Make crossrelease use save_stack_trace_fast() Byungchul Park
2016-09-13  9:45 ` [PATCH v3 09/15] lockdep: Make print_circular_bug() crosslock-aware Byungchul Park
2016-09-13  9:45 ` [PATCH v3 10/15] lockdep: Apply crossrelease to completion operation Byungchul Park
2016-09-13  9:45 ` [PATCH v3 11/15] pagemap.h: Remove trailing white space Byungchul Park
2016-09-13  9:45 ` [PATCH v3 12/15] lockdep: Apply crossrelease to PG_locked lock Byungchul Park
2016-09-13  9:45 ` [PATCH v3 13/15] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2016-09-13  9:45 ` [PATCH v3 14/15] lockdep: Move data used in CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2016-09-13  9:45 ` [PATCH v3 15/15] lockdep: Crossrelease feature documentation Byungchul Park
2016-09-15 17:25   ` Nilay Vaish
2016-09-19  2:59     ` Byungchul Park
2016-09-16 15:47   ` Nilay Vaish
2016-09-19  3:00     ` Byungchul Park
2016-09-20  5:00     ` Byungchul Park
2016-09-13  9:58 ` [FYI] Output of 'cat /proc/lockdep' after applying crossrelease Byungchul Park
2016-11-02  5:42 ` [REVISED DOC on v3] Crossrelease Lockdep Byungchul Park
2016-11-03  8:18   ` Byungchul Park
2016-11-08  2:54     ` Byungchul Park

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