Re: [Qemu-devel] [RFC 0/3] qboot changes for PVH boot

[Liam Merwick]

On 06/12/2018 20:13, Paolo Bonzini wrote:
> On 05/12/18 23:31, Liam Merwick wrote:
> > For certain applications it is desirable to rapidly boot a KVM virtual
> > machine. In cases where legacy hardware and software support within the
> > guest is not needed, QEMU should be able to boot directly into the
> > uncompressed Linux kernel binary with minimal firmware involvement.
> >
> > There already exists an ABI to allow this for Xen PVH guests and the ABI
> > is supported by Linux and FreeBSD:
> >
> >     https://xenbits.xen.org/docs/unstable/misc/pvh.html
> >
> > Details on the Linux changes: https://lkml.org/lkml/2018/4/16/1002
> >
> > This patch series provides qboot support to populate the start_info struct
> > needed by the direct boot ABI and to configure the guest e820 tables to
> > enable QEMU to use that same entry point for booting KVM guests.
> >
> > Usіng the methods/scripts documented by the NEMU team at
> >
> >     https://github.com/intel/nemu/wiki/Measuring-Boot-Latency
> >     https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg00200.html
> >
> > below are some timings measured (vmlinux and bzImage from the same build).
> > Time to get to kernel start is almost halved (95ṁs -> 48ms)
>
> I had a few comments on patch 2, but overall it looks fine.  Can you
> send a pull request on GitHub?

Thanks Paolo.  I have made those changes and submitted a PR:

https://github.com/bonzini/qboot/pull/17

Regards,
Liam


> > QEMU + qboot + vmlinux (PVH + 4.20-rc4)
> >   qemu_init_end: 41.550521
> >   fw_start: 41.667139 (+0.116618)
> >   fw_do_boot: 47.448495 (+5.781356)
> >   linux_startup_64: 47.720785 (+0.27229)
> >   linux_start_kernel: 48.399541 (+0.678756)
> >   linux_start_user: 296.952056 (+248.552515)
> >
> > QEMU + qboot + bzImage:
> >   qemu_init_end: 29.209276
> >   fw_start: 29.317342 (+0.108066)
> >   linux_start_boot: 36.679362 (+7.36202)
> >   linux_startup_64: 94.531349 (+57.851987)
> >   linux_start_kernel: 94.900913 (+0.369564)
> >   linux_start_user: 401.060971 (+306.160058)
> >
> > QEMU + bzImage:
> >   qemu_init_end: 30.424430
> >   linux_startup_64: 893.770334 (+863.345904)
> >   linux_start_kernel: 894.17049 (+0.400156)
> >   linux_start_user: 1208.679768 (+314.509278)
> >
> >
> > Liam Merwick (3):
> >    pvh: Add x86/HVM direct boot ABI header file
> >    pvh: use x86/HVM direct boot ABI
> >    pvh: add benchmark exit point
> >
> >   benchmark.h          |   3 +-
> >   fw_cfg.c             |  79 +++++++++++++++++++++++++++-
> >   include/start_info.h | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++
> >   linuxboot.c          |   2 +-
> >   main.c               |   3 ++
> >   tables.c             |   9 ++++
> >   6 files changed, 239 insertions(+), 3 deletions(-)
> >   create mode 100644 include/start_info.h