On 05/26/2011 09:05 PM, Ingo Molnar wrote:
> > I've added some rwlocks because of what Ingo said yesterday about > adding/removing devices after the first initialization phase. > > Take MMIO lock for example: Since we can now run SMP guests, we may > have multiple MMIO exits (one from each VCPU thread). Each of those > exits leads to searching the MMIO rbtree. > > We can use a mutex to lock it, but it just means that those threads > will be blocked there instead of concurrently searching the MMIO > tree which makes the search linear instead of parallel. > > It's hard to bring 'real' numbers at this stage because the only > 'real' device we have which uses MMIO is the VESA driver, and we > can't really simulate many VCPUs writing to it :) I'd suggest keeping it simple first - rwlocks are nasty and will bounce a cacheline just as much.
Well, this is the first case where tools/kvm can do better than qemu with its global lock, so I think it's worth it.
If lookup scalability is an issue we can extend RCU to tools/kvm/.
Definitely rcu is a perfect patch for mmio dispatch. -- 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
