2015-11-25 03:21+0000, Wu, Feng: > From: Radim Krčmář [mailto:rkrcmar@xxxxxxxxxx] >> The hash function just interprets a subset of vector's bits as a number >> and uses that as a starting offset in a search for an enabled APIC >> within the destination set? >> >> For example: >> The x2APIC destination is 0x00000055 (= first four even APICs in cluster >> 0), the vector is 0b11100000, and bits 10:8 of IntControl are 000. >> >> 000 means that bits 7:4 of vector are selected, thus the vector hash is >> 0b1110 = 14, so the round-robin effectively does 14 % 4 (because we only >> have 4 destinations) and delivers to the 3rd possible APIC (= ID 6)? > > In my current implementation, I don't select a subset of vector's bits as > the number, instead, I use the whole vector number. For software emulation > p. o. v, do we really need to select a subset of the vector's bits as the base > number? What is your opinion? Thanks a lot! I think it's ok to pick any algorithm we like. It's unlikely that software would recognize and take advantage of the hardware algorithm without adding a special treatment for KVM. (I'd vote for the simple pick-first-APIC lowest priority algorithm ... I don't see much point in complicating lowest priority when it doesn't deliver to lowest priority CPU anyway.) I mainly wanted to know what real hardware really does, because there is a lot of alternatives that still fit into the Xeon documentation. -- 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
