tests/vm/openbsd script (etc) excessive CPU usage

From: Peter Maydell <peter.maydell@linaro.org>
To: QEMU Developers <qemu-devel@nongnu.org>
Cc: "Fam Zheng" <famz@redhat.com>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: tests/vm/openbsd script (etc) excessive CPU usage
Date: Sat, 25 Jul 2020 15:20:06 +0100	[thread overview]
Message-ID: <CAFEAcA__RiZoe9qRTT_ZCbm_FmXZMO2MseGkimtL459Uoaoi9A@mail.gmail.com> (raw)

I noticed that when running the BSD VMs, the Python script that launches
QEMU seems to eat CPU:

peter.m+ 19024  0.0  0.0  20296 11692 pts/12   S+   15:04   0:00
   \_ make -C build vm-build-openbsd J=8 V=1
peter.m+ 19858 98.8  0.0 126272 15220 pts/12   Sl+  15:04  12:04
       \_ /usr/bin/python3 -B
/home/peter.maydell/qemu-openbsd/tests/vm/openbsd --debug --jobs 8
--verbose --efi-aarch64
/home/peter.maydell/qemu-openbsd/build/pc-bios/edk2-aarch64-code.fd
--image /home/peter.maydell/.cache/qemu-vm/images/openbsd.img
--snapshot --build-qemu /home/peter.maydell/qemu-openbsd --
peter.m+ 22878  711  3.2 10506236 3192896 pts/12 Sl+ 15:04  86:08
            \_ qemu-system-x86_64 -display none -vga none -chardev
socket,id=mon,path=/var/tmp/qemu-19858-monitor.sock -mon
chardev=mon,mode=control -machine pc -chardev
socket,id=console,path=/var/tmp/qemu-19858-console.sock,server,nowait
-serial chardev:console -nodefaults -m 4G -cpu max -netdev
user,id=vnet,hostfwd=:127.0.0.1:0-:22 -device
virtio-net-pci,netdev=vnet -vnc 127.0.0.1:0,to=20 -smp 8 -enable-kvm
-drive file=/home/peter.maydell/.cache/qemu-vm/images/openbsd.img,snapshot=on,if=none,id=drive0,cache=writeback
-device virtio-blk,drive=drive0,bootindex=0 -drive
file=/home/peter.maydell/qemu-openbsd/build/vm-test-g6q_po6_.tmp/data-993a1.tar,if=none,id=data-993a1,cache=writeback,format=raw
-device virtio-blk,drive=data-993a1,serial=data-993a1,bootindex=1
peter.m+ 29304  0.0  0.0  63612  4996 pts/12   S+   15:05   0:00
           \_ ssh -t -o StrictHostKeyChecking=no -o
UserKnownHostsFile=/dev/null -o ConnectTimeout=1 -p 38491 -i
/home/peter.maydell/qemu-openbsd/build/vm-test-g6q_po6_.tmp/id_rsa -o
SendEnv=https_proxy -o SendEnv=http_proxy -o SendEnv=ftp_proxy -o
SendEnv=no_proxy qemu@127.0.0.1          set -e;         rm -rf
/home/qemu/qemu-test.*         cd $(mktemp -d
/home/qemu/qemu-test.XXXXXX);         mkdir src build; cd src;
tar -xf /dev/rsd1c;         cd ../build         ../src/configure
--cc=cc --python=python3 ;

Notice that process 19858 (the python script) is at 98.8% CPU.
This isn't specific to the OpenBSD script, the other BSD scripts
do this too.

Why is this script using so much CPU when it should basically just be
waiting for the QEMU VM to finish ?

I think this is probably a recent regression, though I'm not certain.

thanks
-- PMM