[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [BUG] Migrate failes between boards with different PMC
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [BUG] Migrate failes between boards with different PMC counts |
Date: |
Mon, 24 Apr 2017 11:27:16 +0100 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
* Daniel P. Berrange (address@hidden) wrote:
> On Mon, Apr 24, 2017 at 10:23:21AM +0100, Dr. David Alan Gilbert wrote:
> > * Zhuangyanying (address@hidden) 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 ?
Yes, they're bits 8..15 of CPUID leaf 0xa
Dave
> 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 :|
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK