On Wed, Mar 25, 2015 at 03:47:39PM -0400, Konrad Rzeszutek Wilk wrote: > Ah nice. That could be spun out as a seperate patch to optimize the existing > ticket locks I presume. Yes I suppose we can do something similar for the ticket and patch in the right increment. We'd need to restructure the code a bit, but its not fundamentally impossible. We could equally apply the head hashing to the current ticket implementation and avoid the current bitmap iteration. > Now with the old pv ticketlock code an vCPU would only go to sleep once and > be woken up when it was its turn. With this new code it is woken up twice > (and twice it goes to sleep). With an overcommit scenario this would imply > that we will have at least twice as many VMEXIT as with the previous code. An astute observation, I had not considered that. > I presume when you did benchmarking this did not even register? Thought > I wonder if it would if you ran the benchmark for a week or so. You presume I benchmarked :-) I managed to boot something virt and run hackbench in it. I wouldn't know a representative virt setup if I ran into it. The thing is, we want this qspinlock for real hardware because its faster and I really want to avoid having to carry two spinlock implementations -- although I suppose that if we really really have to we could. -- 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
