* Sasha Levin <levinsasha928@xxxxxxxxx> wrote: > On Thu, 2011-05-26 at 19:02 +0300, Pekka Enberg wrote: > > On Thu, 26 May 2011, Sasha Levin wrote: > > > Adds a rwlock wrapper which like the mutex wrapper makes rwlock calls > > > similar to their kernel counterparts. > > > > > > Signed-off-by: Sasha Levin <levinsasha928@xxxxxxxxx> > > > > There's no explanation why a mutex isn't sufficient. The pthread > > locking primitives aren't all that great in practice so unless > > you have some correctness issue that requires a rwlock or some > > numbers, I'd prefer you go for a mutex. > > 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. If lookup scalability is an issue we can extend RCU to tools/kvm/. Thanks, Ingo -- 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
