[Qemu-devel] [PATCH v3 0/3] pc: mmap kernel (ELF image) and initrd

[Stefano Garzarella]

In order to reduce the memory footprint when PVH kernel and initrd
are used, we map them into memory instead of reading them.
In this way we can share them between multiple instances of QEMU.

v3:
- Added patch 1 to handle memory-mapped ELFs in rom_add_elf_program() [Paolo]
- Patch 2:
  ~ passed the GMappedFile* to rom_add_elf_program() [Paolo]
  ~ renamed 'GMappedFile *gmf' in 'GMappedFile *mapped_filed' for readability
  ~ set 'data' pointer only if 'file_size > 0' as the original behaviour
    [check-qtest-ppc64 fails without it]
- Patch 3:
  ~ stored the initrd GMappedFile* in PCMachineState to avoid Coverity
    issue [Paolo]
  ~ renamed 'GMappedFile *gmf' in 'GMappedFile *mapped_filed' for readability

v2: https://patchew.org/QEMU/address@hidden/

These are the results using a PVH kernel and initrd (cpio):
- memory footprint (using smem) [MB]
        QEMU              before                   now
    # instances        USS      PSS            USS      PSS
         1           102.0M   105.8M         102.3M   106.2M
         2            94.6M   101.2M          72.3M    90.1M
         4            94.1M    98.0M          72.0M    81.5M
         8            94.0M    96.2M          71.8M    76.9M
        16            93.9M    95.1M          71.6M    74.3M

    Initrd size: 3.0M
    Kernel
        image size: 28M
        sections size [size -A -d vmlinux]:  18.9M

- boot time [ms]
                          before                   now
 qemu_init_end:           63.85                   55.91
 linux_start_kernel:      82.11 (+18.26)          74.51 (+18.60)
 linux_start_user:       169.94 (+87.83)         159.06 (+84.56)

QEMU command used:
./qemu-system-x86_64 -bios /path/to/seabios/out/bios.bin -no-hpet \
    -machine q35,accel=kvm,kernel_irqchip,nvdimm,sata=off,smbus=off,vmport=off \
    -cpu host -m 1G -smp 1 -vga none -display none -no-user-config -nodefaults \
    -kernel /path/to/vmlinux -initrd /path/to/rootfs.cpio \
    -append 'root=/dev/mem0 ro console=hvc0 pci=lastbus=0 nosmap'

Stefano Garzarella (3):
  loader: Handle memory-mapped ELFs
  elf-ops.h: Map into memory the ELF to load
  hw/i386/pc: Map into memory the initrd

 hw/core/loader.c     | 37 +++++++++++++++++++-----
 hw/i386/pc.c         | 17 ++++++++---
 include/hw/elf_ops.h | 68 ++++++++++++++++++++++++++------------------
 include/hw/i386/pc.h |  1 +
 include/hw/loader.h  |  5 ++--
 5 files changed, 88 insertions(+), 40 deletions(-)

-- 
2.20.1