The patch http://libvirt.org/git/?p=libvirt.git;a=commitdiff;h=de0aeafe9ce3eb414c8b5d3aa8995d776a2952de removes invtsc flag in the host-model CPU.
I'm wondering, will it be better to pass args "migratable=no/yes" to qemu, and let qemu complete the remaining work? As that qemu has checked whether it's necessary to use invtsc or not. ---------- "invtsc is available only if using: -cpu host,migratable=no,+invtsc." http://git.qemu.org/?p=qemu.git;a=commit;h=120eee7d1fdb2eba15766cfff7b9bcdc902690b4 ---------- There's another problem, if we do not pass "migratable=no" to qemu. Consider if we set host mode to pass-through --------- <cpu mode='host-passthrough'> </cpu> --------- then the vm->def->cpu->features contains invtsc. however, qemu will automatically remove this cpu flag as that "migration=no" is not passed to it. thus, the guest will not start up. This problem is in fact caused by the patch: http://libvirt.org/git/?p=libvirt.git;a=commit;h=fba6bc47cbcabbe08d42279691efb0dff3b9c997, it forbids guest domain to start up if the host has INVTSC while the guest(qemu) does not. ------------- for (i = 0; def->cpu && i < def->cpu->nfeatures; i++) { virCPUFeatureDefPtr feature = &def->cpu->features[i]; if (feature->policy != VIR_CPU_FEATURE_REQUIRE) continue; if (STREQ(feature->name, "invtsc") && !cpuHasFeature(guestcpu, feature->name)) { virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", _("host doesn't support invariant TSC")); goto cleanup; } } break; -------------- In conclusion: 1 Will it better to pass args "migratable=yes/no" to qemu rather than doing the mask-invtsc job in libvirt? 2 If the guest has "pass-through" cpu mode, then it's unable to start up, because qemu removes invtsc, and vm->def->cpu->features has it. It seems a BUG. -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
