On Thu, Sep 16, 2010 at 12:44:55PM +0200, Michael S. Tsirkin wrote: > On Thu, Sep 16, 2010 at 12:20:47PM +0200, Gleb Natapov wrote: > > On Thu, Sep 16, 2010 at 12:13:39PM +0200, Michael S. Tsirkin wrote: > > > On Thu, Sep 16, 2010 at 12:13:32PM +0200, Gleb Natapov wrote: > > > > On Thu, Sep 16, 2010 at 11:53:10AM +0200, Michael S. Tsirkin wrote: > > > > > On Thu, Sep 16, 2010 at 11:46:03AM +0200, Avi Kivity wrote: > > > > > > On 09/16/2010 11:25 AM, Gleb Natapov wrote: > > > > > > >> > > > > > > >> MSI only appeared in rhel6, older guests still use level interrupts. > > > > > > >So they are already slow for other reasons. > > > > > > > > > > > > > > > > > > > Exactly, for example they need to exit to userspace to ack the > > > > > > interrupt. That's far slower than the workqueue. > > > > > > > > > > Well, this is not exactly comparable: you might get > > > > > same irq asserted multiple times and only deasserted once. > > > > > > > > > Are we talking about level interrupts? Why would you assert level > > > > triggered interrupt multiple times before deasserting it? > > > > > > User of irqfd has no way to know what current interrupt level is. > > > So it has to keep asserting. > > > > > Why can't it keep track of current level? > > This breaks the model: eventfd user is unaware of PCI, levels and such: > it just signals the event. Remember that asserts are done from e.g. vhost-net, > deasserts need to be handled by qemu. > eventfd user implements HW and it knows exactly what type of interrupt this HW generates. -- Gleb. -- 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
