On Mon, 2013-04-22 at 08:52 -0400, Rik van Riel wrote: > On 04/22/2013 07:51 AM, Peter Zijlstra wrote: > > On Sun, 2013-04-21 at 17:12 -0400, Rik van Riel wrote: > >> > >> If we always incremented the ticket number by 2 (instead of 1), then > >> we could use the lower bit of the ticket number as the spinlock. > > > > ISTR that paravirt ticket locks already do that and use the lsb to > > indicate the unlock needs to perform wakeups. > > > > Also, since all of this is virt nonsense, shouldn't it live in the > > paravirt ticket lock code and leave the native code as is? > > Sure, but that is still no reason not to have the virt > implementation be as fast as possible, and share the same > data type as the non-virt implementation. It has to share the same data-type.. > Also, is it guaranteed that the native spin_lock code has > not been called yet before we switch over to the paravirt > functions? > > If the native spin_lock code has been called already at > that time, the native code would still need to be modified > to increment the ticket number by 2, so we end up with a > compatible value in each spin lock's .tickets field, and > prevent a deadlock after we switch over to the paravirt > variant. I thought the stuff already made it upstream, but apparently not; the lastest posting I'm aware of is here: https://lkml.org/lkml/2012/5/2/105 That stuff changes the normal ticket increment as well.. -- 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
