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 <[email protected]>
Signed-off-by: Shaohua Li <[email protected]>

diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index d7c99161bba26a3b484cf5be020707b9fd2d35ab..605cf46c17bd315919e1c4f3425eb9ebc5e89028 100644 (file)
--- 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 a9965f4af4dd391cce6fb3875bd48332560e3598..fcb05305a5a26d4a5394df773ff741520242438c 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 a753ff56670faee6788c8f3c0e2e6d5e13d3a3e1..7e4f7a8ffa8e2adcf6def548c9ddfc4233728547 100644 (file)
--- 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();