On Tue, Mar 04, 2008 at 01:28:24PM -0600, 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.
I fully expected to have to run QEMU with -S and then use cont if I were todo CPU pinning from libvirt. The only info I'd need to get is the PID <-> vCPU mapping data. Then I can use regular Linux taskset capabilities from libvirt to assign the initial pCPU <-> vCPU mapping and finally run 'cont'. > 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. 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. I agree that adding QEMU commands for stuff which Linux already has APIs and tools is a bad idea. QEMU/KVM is much nicer to manage than Xen, precisely because I can already use Linux APIs & process management tools. Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=| ------------------------------------------------------------------------- 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
