Anthony Liguori wrote: > Glauber Costa wrote: >> My main interest is in management tools being able to specify pinning >> set ups at VM creation time. >> >> As I said, it can be done through tools like taskset, but then you'd >> have to know: >> * when are the threads created >> * which thread ids corresponds to each cpu >> >> And of course, for an amount of time, the threads will be running in a >> "wrong" cpu, which may affect workloads running there. (which is a >> case cpu pinning usually tries to address) > > A management tool can start QEMU with -S to prevent any CPUs from > running, query the VCPU=>thread id relationship (modifying info cpus > would be a good thing to do for this), taskset, and then run 'cont' in > the monitor if they desperately need this functionality. However, I > don't think the vast majority of people need this particular functionality.
No, it can't. Because at the time qemu starts, no vcpu -> thread id relationship exists at all. And we don't know when it will. It would be a different story if there were some kind of api that could warn qemu > My feeling is that adding an interface to do this in QEMU encourages > people to not use the existing Linux tools for this or worse yet, to > think they can do a better job than Linux. I agree with you that we should stick with linux tools, and that's why I didn't provide any kind of runtime setting via qemu monitor to do this (with the infrastructure, it would be trivial). taskset will do. > The whole reason this exists > in Xen is that Xen's schedulers were incapable of doing CPU migration > historically (which is no longer true since the credit scheduler). It > was necessary to specify pinning upon creation or you were stuck with > round-robin placement. So libvirt has APIs for this because they were > part of the Xen API because it was needed to get reasonable performance > at some point in time on Xen. I don't think this behavior is useful for > KVM though. Just because Xen does it doesn't imply that we should do it. No, not just because xen does. I do however feel it useful, since starting a vm and then let it run unchanged is definitely an useful use case. And as I tried to show you, I can't see a good way to do that for pinning. > Regards, > > Anthony Liguori > >> >> > ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
