Re: [libvirt] [PATCH 4/7] qemu: Add monitor APIs to fetch CPUID data from QEMU
On Tue, Jul 23, 2013 at 07:32:46PM +0200, Jiri Denemark wrote:
On Tue, Jul 23, 2013 at 19:28:38 +0200, Jiri Denemark wrote:
> On Tue, Jul 23, 2013 at 17:32:42 +0100, Daniel Berrange wrote:
> > On Tue, Jul 23, 2013 at 06:11:33PM +0200, Jiri Denemark wrote:
> > > ---
> > > src/qemu/qemu_monitor.c | 21 +++
> > > src/qemu/qemu_monitor.h | 3 +
> > > src/qemu/qemu_monitor_json.c | 162
+++++++++++++++++++++
> > > src/qemu/qemu_monitor_json.h | 6 +
> > > tests/Makefile.am | 1 +
> > > .../qemumonitorjson-getcpu-empty.data | 2 +
> > > .../qemumonitorjson-getcpu-empty.json | 46 ++++++
> > > .../qemumonitorjson-getcpu-filtered.data | 4 +
> > > .../qemumonitorjson-getcpu-filtered.json | 46 ++++++
> > > .../qemumonitorjson-getcpu-full.data | 4 +
> > > .../qemumonitorjson-getcpu-full.json | 46 ++++++
> > > .../qemumonitorjson-getcpu-host.data | 5 +
> > > .../qemumonitorjson-getcpu-host.json | 45 ++++++
> > > tests/qemumonitorjsontest.c | 74 ++++++++++
> > > 14 files changed, 465 insertions(+)
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-empty.data
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-empty.json
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-filtered.data
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-filtered.json
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-full.data
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-full.json
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-host.data
> > > create mode 100644
tests/qemumonitorjsondata/qemumonitorjson-getcpu-host.json
> >
> > ACK, though I believe the design of this monitor API is flawed
> > because it requires you to re-launch QEMU with different accel
> > args
>
> Not really, this can be used in tcg too. It's just when we want to get
> the data for "host" CPU, we need to enable kvm as tcg knows nothing
> about that CPU. Which makes sense as kvm (the kernel module) influences
> how the "host" CPU will look like.
However, you need to have a CPU to be able to ask for his properties
(which kinda makes sense too) and for that you also need a machine with
type != none. Which makes sense too, as the CPU may differ depending on
machine type (which, however, does not happen for "host" CPU).
In addition to the "-cpu host" KVM initialization problem, this is an
additional problem with the current interfaces provided by QEMU:
1) libvirt needs to query data that depend on chosen machine-type and
CPU model
2) Some machine-type behavior is code and not introspectable data
* Luckily most of the data we need in this case should/will be
encoded in the compat_props tables.
* In either case, we don't have an API to query for machine-type
compat_props information yet.
3) CPU model behavior will be modelled as CPU class behavior. Like
on the machine-type case, some of the CPU-model-specific behavior may
be modelled as code, and not introspectable data.
* However, e may be able to eventually encode most or all of
CPU-model-specific behavior simply as different per-CPU-class
property defaults.
* In either case, we don't have an API for QOM class introspection,
yet.
But there's something important in this case: the resulting CPUID data
for a specific machine-type + CPU-model combination must be always the
same, forever. This means libvirt may even use a static table, or cache
this information indefinitely.
(Note that I am not talking about "-cpu host", here, but about all the
other CPU models)
--
Eduardo