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) 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 -- 1.8.3.1
