README.md: added performance options (resolves linux-sunxi#25)

README.md

@@ -14,3 +14,35 @@ Maintainers:
 * Nicolas Aguirre <aguirre.nicolas@gmail.com>
 * Enrico Butera <ebutera@users.berlios.de>
 * Sergey Lapin <slapin@ossfans.org>
+
+
+
+Performance
+===========
+The default machine settings are meant to be the lowest common denominator, maximizing generality.
+Significantly better performance (2x-3x) can be achieved with the following settings:
+
+**_Allwinner A20_**
+
+For Allwinner A20 (Cubieboard2/CubieTruck), the following tuning options are recommended:
+
+_Enable hardfloat, thumb2 and neon capabilities_
+	DEFAULTTUNE = "cortexa7thf-neon"
+
+This tuning profile takes advantage of the Allwinner A20 Thumb2, hardfloat and neon capabilities.
+Note that it does not compile code with the "-mfpu=neon-vfpv4" flag, although this would even give better performance. Currently there is no way to do this through a tuning profile, but a work-around to do this manually is explained at https://github.com/linux-sunxi/meta-sunxi/issues/25.
+
+_Change CPU governor to ondemand, and tune settings_
+	echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
+	echo 336000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
+	echo 912000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
+	#More aggressive
+	#echo 1008000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
+	echo 40 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
+	echo 200000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
+
+This code changes the default CPU governor from _fantasy_ to _ondemand_, and tunes its settings, as recommended at http://linux-sunxi.org/Cpufreq
+
+For additional discussion, see https://github.com/linux-sunxi/meta-sunxi/issues/25
+
+