In my testing with sysbench in a HVM domU running a linux-4.4 based pvops kernel on a xen-4.7 based dom0 the time does not move forward properly:
There (URL below) is basically code like this: clock_gettime(CLOCK_MONOTONIC, a) do_work clock_gettime(CLOCK_MONOTONIC, b) diff_time(a,b) All 'do_work' does is writing zeros to a block of memory. clock_getres(CLOCK_MONOTONIC) indicates a resolution of 1ns. If 'do_work' takes like 100ns or less: a==b. I think this is something that should not happen. In case of vcpu overcommit this happens also when 'do_work' takes around 800ns. At some point I have also seen cases of time going backward. I can not reproduce this anymore, might have been bugs in my code or the domU.cfg changed. A workaround is booting the domU kernel with 'clocksource=tsc nohz=off highres=off'. Why does this happen? Are the expectations too high? Olaf https://github.com/olafhering/sysbench/compare/master...pv bash autogen.sh make -j bash mem.1K.on.sh
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