raid6: add Kconfig option to skip raid6 benchmarking

Adds CONFIG_RAID6_FORCE_ALGO, which causes the kernel to not benchmark
each raid recovery and syndrome generation algorithm, and instead use
the version selected via Kconfig (CONFIG_RAID6_FORCE_{INT,SSSE3,AVX2}).
In the case, the selected algorithm is not supported by the processor at
runtime, a fallback is used.

TAG_MSFT: lcow

Signed-off-by: Jim Kukunas <james.t.kukunas@linux.intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>

lib/Kconfig

@@ -7,8 +7,7 @@ config BINARY_PRINTF
 
 menu "Library routines"
 
-config RAID6_PQ
-	tristate
+source "lib/raid6/Kconfig"
 
 config BITREVERSE
 	tristate

lib/raid6/Kconfig

@@ -0,0 +1,38 @@
+menu "RAID 6"
+
+config RAID6_PQ
+	tristate
+
+config RAID6_FORCE_ALGO
+	bool "Always use specified recovery algorithm"
+	default n
+	depends on RAID6_PQ
+	help
+		If this option is not set, on every boot the kernel will
+		benchmark each optimized version of the RAID6 recovery and
+		syndrome generation algorithms and will select the one that
+		performs best. Microbenchmarking each version negatively
+		affects boot time.
+
+		Enabling this option skips the benchmark at boot, and
+		instead always uses the algorithm selected. The only exception
+		is if the selected algorithm relies on a cpu feature not
+		supported at runtime. In this case, one of the lower performance
+		fallbacks are used.
+
+choice
+	prompt "RAID6 Recovery Algorithm"
+	default RAID6_FORCE_INT
+	depends on RAID6_FORCE_ALGO
+	---help---
+		Select the RAID6 recovery algorithm to unconditionally use
+
+	config RAID6_FORCE_INT
+		bool "Reference Implementation"
+	config RAID6_FORCE_SSSE3
+		bool "SSSE3"
+	config RAID6_FORCE_AVX2
+		bool "AVX2"
+endchoice
+
+endmenu

lib/raid6/algos.c

@@ -129,6 +129,63 @@ const struct raid6_recov_calls *const raid6_recov_algos[] = {
 #define time_before(x, y) ((x) < (y))
 #endif
 
+#ifdef CONFIG_RAID6_FORCE_ALGO
+/* TODO don't compile in algos that will never be used */
+int __init raid6_select_algo(void)
+{
+	const struct raid6_recov_calls *recov_fallback = &raid6_recov_intx1;
+	const struct raid6_recov_calls *recov_algo;
+	const struct raid6_calls *gen_fallback;
+	const struct raid6_calls *gen_algo;
+
+#if defined(__i386__)
+	gen_fallback = &raid6_intx32;
+#elif defined(__x86_64__)
+	gen_fallback = &raid6_sse2x2;
+#else
+# error "TODO"
+#endif
+
+#if defined(CONFIG_RAID6_FORCE_INT)
+	recov_algo = &raid6_recov_intx1;
+	gen_algo = &raid6_intx32;
+
+#elif defined(CONFIG_RAID6_FORCE_SSSE3)
+	recov_algo = &raid6_recov_ssse3;
+#if defined(__i386__)
+	gen_algo = &raid6_sse2x2;
+#else
+	gen_algo = &raid6_sse2x4;
+#endif
+
+#elif defined(CONFIG_RAID6_FORCE_AVX2)
+	recov_algo = &raid6_recov_avx2;
+
+#if defined(__i386__)
+	gen_algo = &raid6_avx2x2;
+#else
+	gen_algo = &raid6_avx2x4;
+#endif
+
+#else
+#error "RAID6 Forced Recov Algo: Unsupported selection"
+#endif
+
+	if (recov_algo->valid != NULL && recov_algo->valid() == 0)
+		recov_algo = recov_fallback;
+
+	pr_info("raid6: Forced to use recovery algorithm %s\n", recov_algo->name);
+
+	raid6_2data_recov = recov_algo->data2;
+	raid6_datap_recov = recov_algo->datap;
+
+	pr_info("raid6: Forced gen() algo %s\n", gen_algo->name);
+
+	raid6_call = *gen_algo;
+
+	return gen_algo && recov_algo ? 0 : -EINVAL;
+}
+#else
 static inline const struct raid6_recov_calls *raid6_choose_recov(void)
 {
 	const struct raid6_recov_calls *const *algo;
@@ -260,6 +317,7 @@ int __init raid6_select_algo(void)
 
 	return gen_best && rec_best ? 0 : -EINVAL;
 }
+#endif
 
 static void raid6_exit(void)
 {