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diff --git a/docs/07-Linux-cpu-hotplug-howto.txt b/docs/07-Linux-cpu-hotplug-howto.txt new file mode 100755 index 0000000..873a88c --- /dev/null +++ b/docs/07-Linux-cpu-hotplug-howto.txt @@ -0,0 +1,82 @@ +Instructions & Guidelines to use Linux cpu hotplug +================================================== + +A Introduction + + This note describes how the Virtualizer software should + be configured for use with the Linux cpu hotplug + subsystem. It also mentions conditions that both Linux + and the Virtualizer software should fulfil for cpu + hotplug to work. + +B Guidelines + + A cpu hotplug operation involves migration of all tasks + and interrupts from the cpu in question before flushing + the relevant cache level(s) and shutting down the cpu. + A cpu is shutdown by programming the relevant RST_HOLDx + register in the KingFisher System Control Block (KFSCB). + + The Virtualizer software traps accesses to the KFSCB made + by Linux to shutdown a cpu to save its HYP mode context + and request the Secure world to save its own context. It + then proceeds with the shutdown operation as Linux + originally intended. The key assumption made here is that + Linux will access the KFSCB RST_HOLDx registers only + during a cpu hotplug operation. + + It is also assumed that its not possible hotplug cpu0. + Hence, Linux cpu hotplug will work only with the MPx4 + variant of the big.LITTLE FastModels. + + The Virtualizer software is built to switch the payload + software between clusters asynchronously. There is a + possibility of unpredictable behaviour happenning if a + cluster switch is initiated when a cpu hotplug operation + is in progress. Hence the following two conditions need + to be met to be able to use the Virtualizer software in + conjunction with Linux cpu hotplug: + + 1. The Virtualizer software should be built to support + synchronous switching by setting the ASYNC + environment variable to FALSE prior to building it. + For example with the tcsh shell: + + setenv ASYNC FALSE; make + + 2. Linux should invoke a cluster switch explicitly + after ensuring that no cpu hotplug operation is in + progress and vice versa. It can invoke a cluster + switch by using the "HVC #1" assembler instruction + from the relevant code. + +C Instructions + + 1. Build a linux kernel as per the steps listed in + "docs/03-Linux-kernel-build.txt". + The configuration includes support for cpu + hotplug by default. + + 2. Use an existing root filesystem or build a new + one as per the steps listed in + "docs/06-Optional-rootfs-build.txt". + + 3. Place the kernel in the + "bootwrapper/payload/kernel" directory and the + filesystem in the "bootwrapper/payload/fsimg" + directory. Build the Virtualizer software with + support for synchronous switching as mentioned + in B.1. + + 4. Boot the resulting "bootwrapper/img.axf" file + using the "bootwrapper/big-little-mp4.mxscript" + file. At the command prompt, the Linux cpu + hotplug commands to hotplug cpus should work + as expected. For example, to hotplug cpu1 do: + + echo 0 > /sys/devices/system/cpu/cpu1/online + + To bring cpu1 online do: + + echo 1 > /sys/devices/system/cpu/cpu1/online + |