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powerpc: Re-enable dynticks
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Implement arch_irq_work_has_interrupt() for powerpc

Commit 9b01f5b introduced a dependency on "IRQ work self-IPIs" for
full dynamic ticks to be enabled, by expecting architectures to
implement a suitable arch_irq_work_has_interrupt() routine.

Several arches have implemented this routine, including x86 (3010279)
and arm (09f6edd), but powerpc was omitted.

This patch implements this routine for powerpc.

The symptom, at boot (on powerpc systems) with "nohz_full=<CPU list>"
is displayed:

     NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs

after this patch:

     NO_HZ: Full dynticks CPUs: <CPU list>.

Tested against 3.19.

powerpc implements "IRQ work self-IPIs" by setting the decrementer to 1 in
arch_irq_work_raise(), which causes a decrementer exception on the next
timebase tick. We then handle the work in __timer_interrupt().

CC: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Paul A. Clarke <pc@us.ibm.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[mpe: Flesh out change log, fix ws & include guards, remove include of processor.h]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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Paul Clarke authored and Michael Ellerman committed Feb 23, 2015
1 parent c517d83 commit fea559f
Showing 1 changed file with 9 additions and 0 deletions.
9 changes: 9 additions & 0 deletions arch/powerpc/include/asm/irq_work.h
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#ifndef _ASM_POWERPC_IRQ_WORK_H
#define _ASM_POWERPC_IRQ_WORK_H

static inline bool arch_irq_work_has_interrupt(void)
{
return true;
}

#endif /* _ASM_POWERPC_IRQ_WORK_H */

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