From be85f93ae2df32dea0b20908316f1d894c3e0f64 Mon Sep 17 00:00:00 2001
From: Daniel Verkamp <dverkamp@chromium.org>
Date: Mon, 12 Nov 2018 15:26:52 -0800
Subject: [PATCH] lib/raid6: add option to skip algo benchmarking
Git-commit: be85f93ae2df32dea0b20908316f1d894c3e0f64
Patch-mainline: v5.0-rc1
References: bsc#1166003

This is helpful for systems where fast startup time is important.
It is especially nice to avoid benchmarking RAID functions that are
never used (for example, BTRFS selects RAID6_PQ even if the parity RAID
mode is not in use).

This saves 250+ milliseconds of boot time on modern x86 and ARM systems
with a dozen or more available implementations.

The new option is defaulted to 'y' to match the previous behavior of
always benchmarking on init.

Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Coly Li <colyli@suse.de>

---
 include/linux/raid/pq.h | 3 +++
 lib/Kconfig             | 8 ++++++++
 lib/raid6/algos.c       | 5 +++++
 3 files changed, 16 insertions(+)

diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index d7c99161bba2..605cf46c17bd 100644
--- a/include/linux/raid/pq.h
+++ b/include/linux/raid/pq.h
@@ -70,6 +70,9 @@ extern const char raid6_empty_zero_page[PAGE_SIZE];
 #define MODULE_DESCRIPTION(desc)
 #define subsys_initcall(x)
 #define module_exit(x)
+
+#define IS_ENABLED(x) (x)
+#define CONFIG_RAID6_PQ_BENCHMARK 1
 #endif /* __KERNEL__ */
 
 /* Routine choices */
diff --git a/lib/Kconfig b/lib/Kconfig
index a9965f4af4dd..fcb05305a5a2 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -10,6 +10,14 @@ menu "Library routines"
 config RAID6_PQ
 	tristate
 
+config RAID6_PQ_BENCHMARK
+	bool "Automatically choose fastest RAID6 PQ functions"
+	depends on RAID6_PQ
+	default y
+	help
+	  Benchmark all available RAID6 PQ functions on init and choose the
+	  fastest one.
+
 config BITREVERSE
 	tristate
 
diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
index a753ff56670f..7e4f7a8ffa8e 100644
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -163,6 +163,11 @@ static inline const struct raid6_calls *raid6_choose_gen(
 			if ((*algo)->valid && !(*algo)->valid())
 				continue;
 
+			if (!IS_ENABLED(CONFIG_RAID6_PQ_BENCHMARK)) {
+				best = *algo;
+				break;
+			}
+
 			perf = 0;
 
 			preempt_disable();
-- 
2.25.0