boot-qemu.sh: Support booting ARMv7 kernels under KVM on AArch64 hosts#52
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nathanchance merged 1 commit intoJan 13, 2022
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Marc Zyngier took a look and said this LGTM, though the host will be told the guest is ARMv8, so the commit message may want to s/ARMv7/32b ARM/. |
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I thought about saying 32-bit ARM in the commit message but I don't think we can do this scheme for |
It is possible to use KVM on AArch64 hosts to boot ARMv7 kernels, which
can result in a significant amount of speed up. On a Raspberry Pi 4:
Benchmark 1: boot-qemu.sh
Time (mean ± σ): 3.879 s ± 0.041 s [User: 1.389 s, System: 0.405 s]
Range (min … max): 3.839 s … 3.982 s 20 runs
Benchmark 2: boot-qemu.sh --no-kvm
Time (mean ± σ): 17.997 s ± 0.091 s [User: 15.614 s, System: 0.422 s]
Range (min … max): 17.850 s … 18.200 s 20 runs
Summary
'boot-qemu.sh' ran
4.64 ± 0.05 times faster than 'boot-qemu.sh --no-kvm'
However, the host must support 32-bit EL1, which is not always true so
we need to add a small C program to check for it before using
'aarch64=off' + '-enable-kvm'. This has no detectable overhead on a
system that does not support it.
Benchmark 1: boot-qemu.sh (with check)
Time (mean ± σ): 6.148 s ± 0.027 s [User: 3.944 s, System: 0.219 s]
Range (min … max): 6.098 s … 6.193 s 20 runs
Benchmark 2: boot-qemu.sh (without check)
Time (mean ± σ): 6.137 s ± 0.029 s [User: 3.981 s, System: 0.170 s]
Range (min … max): 6.079 s … 6.208 s 20 runs
Summary
'boot-utils-ro' ran
1.00 ± 0.01 times faster than 'boot-utils'
Link: https://fedoraproject.org/wiki/Architectures/AArch64/Booting_a_32-Bit_QEMU_image
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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Okay, I see the part that was a little confusing. I adjusted the commit message ( |
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It is possible to use KVM on AArch64 hosts to boot ARMv7 guests, which
can result in a significant amount of speed up. On a Raspberry Pi 4:
However, the host must support 32-bit EL1, which is not always true so we need
to add a small C program to check for it before using 'aarch64=off' +
'-enable-kvm'. This has no detectable overhead on a system that does not
support it.
Link: https://fedoraproject.org/wiki/Architectures/AArch64/Booting_a_32-Bit_QEMU_image