On Thu, 04 Dec 2008 16:37:41 -0800 (PST) David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Paul Mackerras <paulus@xxxxxxxxx> > Date: Fri, 5 Dec 2008 11:33:31 +1100 > > > This is going to be a huge problem, at least on powerpc, because it > > means that the kernel will have to know which events can be counted > > on which counters and what values need to be put in the control > > registers to select them. > > Sparc64 is the same. > > > The situation will be even worse with POWER5 and POWER6, where the > > event selection logic is very complex, with multiple layers of > > multiplexers. I really really don't want the kernel to have to know > > about all that. > > Niagara2 has deep multiplexing and sub-event masking too. > > I really appreciated how perfmon kept all of those details > in userspace. I would like to respectfully disagree with this some. The kernel needs to abstract hardware to some degree for userspace. The problem in this case is that userspace can't really do a better job, in fact it can only do a worse job since it lacks the coordination capability of knowing it has full control of all the hardware registers. I am sure the corner cases you're talking about are nasty, I just don't think they are less nasty when dealt with in userspace. Sure the kernel might be simpler, but the system as a whole sure is not. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
