On Mon, Apr 24, 2017 at 10:23:21AM +0100, Dr. David Alan Gilbert wrote: > * Zhuangyanying (ann.zhuangyany...@huawei.com) wrote: > > Hi all, > > > > Recently, I found migration failed when enable vPMU. > > > > migrate vPMU state was introduced in linux-3.10 + qemu-1.7. > > > > As long as enable vPMU, qemu will save / load the > > vmstate_msr_architectural_pmu(msr_global_ctrl) register during the > > migration. > > But global_ctrl generated based on cpuid(0xA), the number of > > general-purpose performance > > monitoring counters(PMC) can vary according to Intel SDN. The number of PMC > > presented > > to vm, does not support configuration currently, it depend on host cpuid, > > and enable all pmc > > defaultly at KVM. It cause migration to fail between boards with different > > PMC counts. > > > > The return value of cpuid (0xA) is different dur to cpu, according to Intel > > SDN，18-10 Vol. 3B: > > > > Note: The number of general-purpose performance monitoring counters (i.e. N > > in Figure 18-9) > > can vary across processor generations within a processor family, across > > processor families, or > > could be different depending on the configuration chosen at boot time in > > the BIOS regarding > > Intel Hyper Threading Technology, (e.g. N=2 for 45 nm Intel Atom > > processors; N =4 for processors > > based on the Nehalem microarchitecture; for processors based on the Sandy > > Bridge > > microarchitecture, N = 4 if Intel Hyper Threading Technology is active and > > N=8 if not active). > > > > Also I found, N=8 if HT is not active based on the broadwell，, > > such as CPU E7-8890 v4 @ 2.20GHz > > > > # ./x86_64-softmmu/qemu-system-x86_64 --enable-kvm -smp 4 -m 4096 -hda > > /data/zyy/test_qemu.img.sles12sp1 -vnc :99 -cpu kvm64,pmu=true -incoming > > tcp::8888 > > Completed 100 % > > qemu-system-x86_64: error: failed to set MSR 0x38f to 0x7000000ff > > qemu-system-x86_64: /data/zyy/git/test/qemu/target/i386/kvm.c:1833: > > kvm_put_msrs: > > Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed. > > Aborted > > > > So make number of pmc configurable to vm ? Any better idea ? > > Coincidentally we hit a similar problem a few days ago with -cpu host - it > took me > quite a while to spot the difference between the machines was the source > had hyperthreading disabled. > > An option to set the number of counters makes sense to me; but I wonder > how many other options we need as well. Also, I'm not sure there's any > easy way for libvirt etc to figure out how many counters a host supports - > it's not in /proc/cpuinfo.
We actually try to avoid /proc/cpuinfo whereever possible. We do direct CPUID asm instructions to identify features, and prefer to use /sys/devices/system/cpu if that has suitable data Where do the PMC counts come from originally ? CPUID or something else ? Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
