On Wed, Jul 18, 2012 at 01:13:06PM -0600, Alex Williamson wrote: > On Wed, 2012-07-18 at 13:07 -0600, Alex Williamson wrote: > > On Wed, 2012-07-18 at 15:42 -0300, Marcelo Tosatti wrote: > > > On Wed, Jul 18, 2012 at 06:58:24PM +0300, Michael S. Tsirkin wrote: > > > > > > > > > Back to original point though current > > > > > > > > > situation is that calling kvm_set_irq() under spinlock is not worse for > > > > > > > > > scalability than calling it not under one. > > > > > > > > > > > > > > > > Yes. Still the specific use can just use an atomic flag, > > > > > > > > lock+bool is not needed, and we won't need to undo it later. > > > > > > > > > > > > > > > > > > > > > Actually, no, replacing it with an atomic is racy. > > > > > > > > > > > > > > CPU0 (inject) CPU1 (EOI) > > > > > > > atomic_cmpxchg(&asserted, 0, 1) > > > > > > > atomic_cmpxchg(&asserted, 1, 0) > > > > > > > kvm_set_irq(0) > > > > > > > kvm_set_irq(1) > > > > > > > eventfd_signal > > > > > > > > > > > > > > The interrupt is now stuck on until another interrupt is injected. > > > > > > > > > > > > > > > > > > > Well EOI somehow happened here before interrupt so it's a bug somewhere > > > > > > else? > > > > > > > > > > Interrupts can be shared. We also can't guarantee that the guest won't > > > > > write a bogus EOI to the ioapic. The irq ack notifier doesn't filter on > > > > > irq source id... I'm not sure it can. > > > > > > > > I guess if Avi OKs adding another kvm_set_irq under spinlock that's > > > > the best we can do for now. > > > > > > Why can't a mutex be used instead of a spinlock again? > > > > eventfd_signal calls the inject function from atomic context. > > Actually, that's called from a workq. I'll have to switch it back and > turn on lockdep to remember why I couldn't sleep there. I'll try to fix kvm_set_irq so it returns 0 if level was already 0. Then you do not need extra state. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
