On 14/11/2022 23.58, Pawel Polawski wrote:
Hi Everyone,
I am trying to check qemu virtual cpu boundaries when running a custom
edk2 based firmware build. For that purpose I want to run qemu with more
than 1024 vCPU:
$QEMU
-accel kvm
-m 4G
-M q35,kernel-irqchip=on,smm=on
-smp cpus=1025,maxcpus=1025 -global mch.extended-tseg-mbytes=128
-drive if=pflash,format=raw,file=${CODE},readonly=on
-drive if=pflash,format=raw,file=${VARS}
-chardev stdio,id=fwlog
-device isa-debugcon,iobase=0x402,chardev=fwlog "$@"
The result is as follows:
QEMU emulator version 7.0.50 (v7.0.0-1651-g9cc1bf1ebc-dirty)
Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project developers
qemu-system-x86_64: -accel kvm: warning: Number of SMP cpus requested (1025)
exceeds the recommended cpus supported by KVM (8)
Number of SMP cpus requested (1025) exceeds the maximum cpus supported by
KVM (1024)
It is not clear to me if I am hitting qemu limitation or KVM limitation here.
I have changed hardcoded 1024 limits in hw/i386/* files but the limitation
is still presented.
Can someone advise what I should debug next looking for those vCPU limits?
Well, the error message says it: There is a limitation in KVM, i.e. in the
kernel code, too. I think it is KVM_MAX_VCPUS in the file
arch/x86/include/asm/kvm_host.h of the Linux kernel sources... so if you're
brave, you might want to increase that value there and rebuild your own
kernel. Not sure whether that works, though.
Thomas
