other: 0.927 semantic: 0.919 graphic: 0.909 debug: 0.906 permissions: 0.891 network: 0.874 device: 0.865 PID: 0.864 performance: 0.863 vnc: 0.861 files: 0.852 KVM: 0.849 boot: 0.843 socket: 0.810 QEMU is not allowing multiple cores with mips architecture I may have found a bug as when trying to boot up an QEMU VM with the following command: "qemu-system-mips -M malta -m 512 -hda hda.img -kernel vmlinux-4.19.0-10-4kc-malta -initrd initrd.img-4.19.0-10-4kc-malta -append "root=/dev/sda1 console=ttyS0" -nographic -device e1000,netdev=user.0 -netdev user,id=user.0,hostfwd=tcp::5555-:22 -smp cores=12,threads=1,sockets=1", it will use up all of the CPU cores on the host, but not bootup? Kernel log also shows: [ 100.303136] perf: interrupt took too long (2506 > 2500), lowering kernel.perf_event_max_sample_rate to 79750 [ 107.656869] perf: interrupt took too long (3195 > 3132), lowering kernel.perf_event_max_sample_rate to 62500 [ 117.668390] perf: interrupt took too long (4033 > 3993), lowering kernel.perf_event_max_sample_rate to 49500 [ 217.166763] perf: interrupt took too long (5126 > 5041), lowering kernel.perf_event_max_sample_rate to 39000 [ 231.910132] perf: interrupt took too long (6445 > 6407), lowering kernel.perf_event_max_sample_rate to 31000 [ 250.170677] perf: interrupt took too long (8087 > 8056), lowering kernel.perf_event_max_sample_rate to 24500 [ 285.391451] perf: interrupt took too long (10126 > 10108), lowering kernel.perf_event_max_sample_rate to 19750 [ 778.588911] perf: interrupt took too long (12770 > 12657), lowering kernel.perf_event_max_sample_rate to 15500 [ 1554.825129] perf: interrupt took too long (15982 > 15962), lowering kernel.perf_event_max_sample_rate to 12500 [ 1622.838910] hrtimer: interrupt took 14758063 ns [ 1712.932777] INFO: NMI handler (perf_event_nmi_handler) took too long to run: 0.000 msecs [ 1712.932780] perf: interrupt took too long (59793 > 19977), lowering kernel.perf_event_max_sample_rate to 3250 System details: OS: Ubuntu 20.04 QEMU emulator version 4.2.0 (Debian 1:4.2-3ubuntu6.3) Hi Skyler, mips emulation is rather rare - so there is always a chance that something broke without being recognized at first. For a start let me ask a few questions to corner the issue: 1. did that work before and is a regression in the qemu 4.2 of Ubuntu? 2. check other versions - could you try the same with qemu 3.1 (Bionic) and 5.0 (groovy) of Ubuntu if it is the same? 3. after we know of the above if new/old versions were ok it could be worth checking pristine upstream qemu builds to see if any delta in Ubuntu has to be fixed. Depending on your time and ability to do so would you be able to build from tags of https://git.qemu.org/?p=qemu.git? (TL;DR; add deb-src lines in /etc/apt/sources.list, apt build-dep qemu; In general maybe attach the kernel/initrd of your test so others can try the same. I assume you used something like http://ftp.debian.org/debian/dists/stable/main/installer-mips/current/images/malta/netboot/ ? Once that is sorted we know better if we look at a "how to use question" or an actual bug - and for the latter if it is a regression of some sort (which would make us hunt for the offending change). I was quickly giving things a check but don't have the time to do the full matrix: The old bits from https://people.debian.org/~aurel32/qemu/mipsel/ $ qemu-system-mips64el -M malta -kernel vmlinux-3.2.0-4-4kc-malta -nographic -curses Later the kernels are more obviously split (mipsel/mips64/mips64el) build at https://people.debian.org/~jcowgill/qemu-mips/ I can get to run with: $ qemu-system-mips64el -M malta -cpu MIPS64R2-generic -m 2G -kernel vmlinux-4.15.0-1-5kc-malta.mips64el.sid -nographic -curses $ qemu-system-mips64el -M malta -cpu MIPS64R2-generic -m 2G -kernel vmlinux-4.15.0-1-5kc-malta.mipsel.sid -nographic -curses $ qemu-system-mips64 -M malta -cpu MIPS64R2-generic -m 2G -kernel vmlinux-4.15.0-1-5kc-malta.mips.sid -nographic -curses Zoning in to something close to your kernel that you've tried from http://ftp.debian.org/debian/dists/stable/main/installer-mips/current/images/malta/netboot/ works with: $ qemu-system-mips64 -M malta -cpu MIPS64R2-generic -m 2G -kernel vmlinux-4.19.0-10-4kc-malta -nographic -curses From here I was slowly getting more similar to your commandline. Sill works: $ qemu-system-mips -M malta -m 2G -kernel vmlinux-4.19.0-10-4kc-malta -nographic -curses add initrd: $ qemu-system-mips -M malta -m 2G -kernel vmlinux-4.19.0-10-4kc-malta -initrd initrd-4.19.0-10-4kc-$malta.gz -nographic -curses Add net: $ qemu-system-mips -M malta -m 2G -kernel vmlinux-4.19.0-10-4kc-malta -initrd initrd-4.19.0-10-4kc-malta.gz -nographic -curses -nographic -device e1000,netdev=user.0 -netdev user,id=user.0,hostfwd=tcp::5555-:22 reduce memory: $ qemu-system-mips -M malta -m 512 -kernel vmlinux-4.19.0-10-4kc-malta -initrd initrd-4.19.0-10-4kc-malta.gz -nographic -curses -nographic -device e1000,netdev=user.0 -netdev user,id=user.0,hostfwd=tcp::5555-:22 kernel commandline: $ qemu-system-mips -M malta -m 512 -kernel vmlinux-4.19.0-10-4kc-malta -initrd initrd-4.19.0-10-4kc-malta.gz -nographic -curses -nographic -device e1000,netdev=user.0 -netdev user,id=user.0,hostfwd=tcp::5555-:22 -append "root=/dev/sda1 console=ttyS0" All that worked, what got it stuck was the smp option that you used. -smp 1 works -smp 2 works -smp 3 stuck -smp 4 stuck qemu-system-mips: /build/qemu-BQ4hMP/qemu-4.2/hw/acpi/cpu.c:198: cpu_hotplug_hw_init: Assertion `mc->possible_cpu_arch_ids' failed. Aborted (core dumped) -smp 4 stuck (retry) [ 0.000000] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: (null) With more memory I get slightly further until stuck, up to -smp 12 things won't get better. Not sure how good/bad smp is in emulated mips - we are back to my initial question - did this work in the past and regressed - or is it instead an upstream feature request for (better) mips emu SMP? These are old, but might still be true: https://lists.gnu.org/archive/html/qemu-devel/2013-06/msg04436.html https://qemu-devel.nongnu.narkive.com/m6BNDsfR/does-qemu-support-mips-smp2-malta-board https://