Gerd Knorr wrote:
> Gerd Knorr wrote:
> 
>> i.e. something like this (as basic idea, patch is far away from doing 
>> anything useful ...)?
> 
> Adapting $subject to the actual topic, so other lkml readers can catch 
> up ;)
> 
> Ok, here new version of the SMP alternatives patch.  It features:

Now, some days hacking & debugging and kernel crashing later I have 
something more than just proof-of-concept ;)

Modules are supported now, fully modularized distro kernel works fine 
with it.  If you have a kernel with HOTPLUG_CPU compiled you can 
shutdown the second CPU of your dual-processor system via sysfs (echo 0 
 > /sys/devices/system/cpu/cpu1/online) and watch the kernel switch over 
to UP code without lock-prefixed instructions and simplified spinlocks, 
then power up the second CPU again (echo 1 > /sys/...) and watch it 
patching back in the SMP locking.

For testing & benchmarking purposes I've put also in two (temporary) 
sysrq's to switch between UP and SMP bits without booting/shutting down 
the second CPU.  That one breaks non-i386 builds which are trivially 
fixable by just dropping the drivers/char/sysrq.c changes ;)

enjoy,

   Gerd