On Mon, 2012-08-06 at 13:40 +0300, Avi Kivity wrote: > On 08/06/2012 01:38 PM, Avi Kivity wrote: > > > Regarding the implementation, instead of a linked list, would an array > > of counters parallel to the bitmap make it simpler? > > Or even, replace the bitmap with an array of counters. I'm not sure a counter array is what we're really after. That gives us reference counting for the irq source IDs, but not the key->gsi lookup. It also highlights another issue, that we have a limited set of source IDs. Looks like we have BITS_PER_LONG IDs, with two already used, one for the shared userspace ID and another for the PIT. How happy are we going to be with a limit of 62 level interrupts in use at one time? It's arguably a reasonable number since the most virtualization friendly devices (sr-iov VFs) don't even support this kind of interrupt. It's also very wasteful allocating an entire source ID for a single GSI within that source ID. PCI supports interrupts A, B, C, and D, which, in the most optimal config, each go to different GSIs. So we could theoretically be more efficient in our use and allocation of irq source IDs if we tracked use by the source ID, gsi pair. That probably makes it less practical to replace anything at the top level with a counter array. The key that we pass back is currently the actual source ID, but we don't specify what it is, so we could split it and have it encode a 16bit source ID plus 16 bit GSI. It could also be an idr entry. Michael, would the interface be more acceptable to you if we added separate ioctls to allocate and free some representation of an irq source ID, gsi pair? For instance, an ioctl might return an idr entry for an irq source ID/gsi object which would then be passed as a parameter in struct kvm_irqfd and struct kvm_eoifd so that the object representing the source id/gsi isn't magically freed on it's own. This would also allow us to deassign/close one end and reconfigure it later. Thanks, Alex -- 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
