lib/raid6: add option to skip algo benchmarking

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>
[jhoon20.kim: backport from mainline for the fast kernel startup]

Change-Id: I38c270c413d60de65f27cf9c95d44bb2e2d07ac2
Signed-off-by: Junghoon Kim <jhoon20.kim@samsung.com>

diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index 8dfaa2ce2e956e0037c469daed8586cb9a94bc68..db8fc96b843ed2996bfa37bc5a6129342b25442e 100644 (file)
--- a/include/linux/raid/pq.h
+++ b/include/linux/raid/pq.h
@@ -67,6 +67,9 @@ 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 5637c9a1017385797f7c683ec529d3231afbaf14..c61757d405c47d138a781c62e12b1f5f5dcb2771 100644 (file)
--- 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 6d7316fe9f30207d83bfe6f086ca98984040207d..1da2445367f968c6f655db133ed1ce9072d0cdc6 100644 (file)
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -131,6 +131,11 @@ 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();