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>
[sw0312.kim: cherry-pick mainline commit be85f93ae2df to skip unnecessary raid6 benchmark during booting]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I70256f5cbfb61c0033a16d2eb57e10e0dd1e6768

diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index 4d57bba..872fd30 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 8deab4f..2614753 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 7857049..62aeb8d 100644 (file)
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -159,6 +159,11 @@ 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();