On Wed, 2009-09-16 at 22:33 +0530, Vaidyanathan Srinivasan wrote: > * Peter Zijlstra <a.p.zijls...@chello.nl> [2009-09-16 18:35:16]: > > > On Wed, 2009-09-16 at 21:54 +0530, Dipankar Sarma wrote: > > > > > No, for this specific case, latency isn't an issue. The issue is - > > > how do we cede unused vcpus to hypervisor for better energy management ? > > > Yes, it can be done by a hypervisor manager telling the kernel to > > > offline and make a bunch of vcpus "inactive". It does have to choose > > > offline (release vcpu) vs. inactive (cede but guranteed if needed). > > > The problem is that long ago we exported a lot of hotplug stuff to > > > userspace through the sysfs interface and we cannot do something > > > inside the kernel without keeping the sysfs stuff consistent. > > > This seems like a sane way to do that without undoing all the > > > virtual cpu hotplug infrastructure in different supporting archs. > > > > I'm still not getting it.. > > > > Suppose we have some guest, it booted with 4 cpus. > > > > We then offline 2 of them. > > > > Apparently this LPAR binds guest cpus to physical cpus? > > So we use a hypervisor interface to reclaim these 2 offlined cpus and > > re-assign them to some other guest. > > > > So far so good, right? > > > > Now if you were to try and online the cpus in the guest, it'd fail > > because the cpus aren't backed anymore, and the hot-plug simply > > times-out and fails. > > > > And we're still good, right? > > The requirement differ here. If we had offlined 2 vCPUs for the > purpose of system reconfiguration, the expected behavior with offline > interface will work right. However the proposed cede interface is > needed when we want them to temporarily go away but still come back > when we do an online. We want the online to always succeed since the > backing physical resources are not relinquished. The proposed > interface facilitates offline without relinquishing the physical > resources assigned to LPARs.
Then make that the platform default and leave the lpar management to whatever pokes at the lpar? _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev