On Wed, Apr 04, 2012 at 11:44:23AM +0300, Avi Kivity wrote: > On 04/04/2012 11:38 AM, Michael S. Tsirkin wrote: > > > > > > > > > > > A performance note: delivering an interrupt needs to search all vcpus > > > > for an APIC ID match. The previous plan was to cache (or pre-calculate) > > > > this lookup in the irq routing table. Now it looks like we'll need a > > > > separate cache for this. > > > > > > As this is non-existent until today, we don't regress here. And it can > > > still be added on top later on, transparently. > > > > I always worry about hash collisions and the cost of > > calculating good hash functions. > > > > We could instead return an index in the cache on injection, maintain in > > userspace and use it for fast path on the next injection. > > Ahem, that is almost the existing routing table to a T. > > > Will make it easy to use an array index instead of a hash here, > > and fallback to a slower ID lookup on mismatch. > > Need a free ioctl so we can reuse IDs. No, it could be kernel controlled not userspace controlled. We get both and address and an index: if (table[u.i].addr == u.addr && table[u.i].data == u.data) { return table[u.i].id; } u.i = find_lru_idx(&table); table[u.i].addr = u.addr; table[u.i].data = u.data; table[u.i].id = find_id(u.addr, u.data); return table[u.i].id; > > Until we do have this fast path we can just fill this value with zeros, > > so kernel patch (almost) does not need to change for this - > > just the header. > > Partially implemented interfaces invite breakage. Hmm true. OK scrap this idea then, it's not clear whether we are going to optimize this anyway. > > -- > I have a truly marvellous patch that fixes the bug which this > signature is too narrow to contain. -- 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