After reports about degraded performance after a PV domU was migrated from one dom0 to another it turned out that this issue happens with every version of Xen and every version of domU kernel.
The used benchmark is 'sysbench memory'. I hacked it up to show how long the actual work takes, and that loop takes longer to execute after the domU is migrated. In my testing the loop (memory_execute_event) takes about 1200ns, after migration it takes about 1500ns. It just writes 0 to an array of memory. In total sysbench reports 6500 MiB/sec, after migration its just 3350 MiB/sec. The source of the modified test can be found here: https://github.com/olafhering/sysbench/compare/master...pv This happens on several hosts. NUMA or not makes no difference. CPU pinning or not makes no difference. Pinning of the test pthreads makes no difference. It was initially reported with xen-4.4, I see it with staging too. The guest kernel makes no difference, several variants of xenlinux or pvops based show the slowdown. Also live migration to localhost is affected. The domU.cfg looks like that: name='pv' memory=1024 vcpus=4 cpus=[ "4", "5", "6", "7" ] disk=[ 'file:/disk0.raw,xvda,w', ] vif=[ 'bridge=br0,type=netfront', ] vfb=[ 'type=vnc,vncunused=1,keymap=de', ] serial="pty" kernel="/usr/lib/grub2/x86_64-xen/grub.xen" Xen is booted with "console=com1 com1=115200 loglvl=all guest_loglvl=all dom0_max_vcpus=2 dom0_vcpus_pin=on". I wonder what the cause might be, and how to check where the time is spent. Olaf
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