On 2012-04-04 13:50, Avi Kivity wrote: > On 04/04/2012 01:48 PM, Jan Kiszka wrote: >>> >>> I'm not so sure anymore. Sorry about the U turn, but remind me why? In >>> the long term it will be slower. >> >> Likely not measurably slower. If you look at a message through the arch >> glasses, you can usually spot the destination directly, specifically if >> a message targets a single processor - no need for hashing and table >> lookups in the common case. > > Not on x86. The APIC ID is guest-provided. ...but is still a rather stable mapping on the physical ID. > In x2apic mode it can be > quite large. Yes, but then you can at least hash/search/cache inside that group only, with a smaller scope. > >> In contrast, the maintenance costs for the current explicit route based >> model are significant as we see now. >> > > You mean in amount of code in userspace? That doesn't get solved since > we need to keep compatibility. We do not need to track MSI origins to correlate them with routes (with the exception of 3 special devices: vhost-based virtio, kvm device assignment, and vfio device assignment). We emulate this centrally with a hand full of LOC in the kvm layer, and we bypass it with the advent of a direct injection API. Compare this to my original series that introduced MSIRoutingCaches to cope with the current kernel API. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
