On Tue, 2010-04-20 at 17:17 -0500, Brian King wrote: > In stress testing enabling and disabling of SMT, we are regularly > seeing the badness warning below. Looking through the cpu offline > path, this is what I see: > > 1. stop_cpu: IRQ's get disabled > 2. pseries_cpu_disable: set cpu offline (no barriers after this) > 3. xics_migrate_irqs_away: Remove ourselves from the GIQ, but still allow > IPIs > 4. stop_cpu: IRQ's get enabled again (local_irq_enable) > > It looks to me like there is plenty of opportunity between 1 and 2 for > an IPI to get queued, resulting in the badness below. Is there something > in xics_migrate_irqs_away that should clear any pending IPIs? If there > is, maybe the solution is as simple as adding a barrier after marking > the cpu offline. Or is the warning bogus and we should just remove it?
It looks like xics_migrate_irqs_away() doesn't do anything about IPIs, at least the comment says "Allow IPIs again". So I don't see what's to stop you just taking another IPI after you reenable interrupts in stop_cpu(). Maybe xics_ipi_dispatch() should just return if the cpu is offline? cheers
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