| | Subject | mutex vs. local irqs (Was: 2.6.18 -mm merge plans) | | From | Benjamin Herrenschmidt <> | | Date | Wed, 07 Jun 2006 13:52:58 +1000 |
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> work-around-ppc64-bootup-bug-by-making-mutex-debugging-save-restore-irqs.patch > kernel-kernel-cpuc-to-mutexes.patch > > ug. We cannot convert the cpu.c semaphore into a mutex until we work out > why power4 goes titsup if you enable local interrupts during boot.
What is the exact problem ? Some mutex is forcing local irqs enabled before init_IRQ() ? (Before the normal enabling of IRQ done by init/main.c just after init_IRQ() more precisely ?)
This is bad for any architecture. Basically, at this point, the interrupt controller can be in _any_ state, with possible pending interrupts for whatever sources, etc...
As we discussed before, that problem should really be fixed in the mutex code by not hard-enabling.
There is an incredible amount of crap that could be cleaned up for example by re-ordering a bit the init code and making things like slab available before init_IRQ/time_init etc... but all of those will break because of that.
In addition, even without that re-ordering, I'm pretty sure we are hitting semaphores/mutexes early, before init_IRQ(), already and if not in generic code, in arch code somewhere down the call stacks.
I don't think that whole pile of problems lurking around the corner is worth the couple of cycles saved by hard-enabling irq in the mutex instead of doing a save/restore.
Ben.
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