On Thu, 11 Apr 2019 at 06:56, Alex Bennée alex.bennee@linaro.org wrote:

Dan Rue dan.rue@linaro.org writes:

...

Hi Alex -

I'm wondering if you can help or suggest the best way to report an issue we found while adding perf testing to LKFT.

https://bugs.linaro.org/show_bug.cgi?id=4320

This issue is only seen on 4.4 (we test 4.4, 4.9, 4.14, 4.19, mainline, next), and only on qemu/x86_64 and qemu/i386 (those architectures work fine when run on hardware). Reproducer is simple, just run 'perf record -e cycles -o perf-lava-test.data ls -a'.

Whats the command line for running QEMU?

/usr/bin/qemu-system-x86_64 -cpu host -enable-kvm -nographic -net nic,model=virtio,macaddr=DE:AD:BE:EF:66:08 -net tap -m 1024 -monitor none -drive format=raw,file=rpb-console-image-lkft-intel-corei7-64-20190326043926-446.hddimg,if=virtio -m 4096 -smp 4 -nographic -drive format=qcow2,file=lava-guest.qcow2,media=disk,if=virtio

And Linux version 4.4.178-rc1 qemu-system-x86, installed at version: 1:2.12.0-1, host architecture: amd64

If you are running the guests under KVM it could be related to the CPU type/flags being exposed to the guests and the requisite performance counters the PMU system will be accessing. It may be that KVM is trapping the PMU access but not properly emulating it.

If it's under TCG (emulation) then it will depend on if the x86 cpu emulation is complete enough to handle all the various counters. The x86 TCG front-end is one of the less complete front-ends, certainly for more modern instructions and cpu features.

I'm currently on holiday so I'll look in more detail once I'm back.

- Naresh

...

Thanks, Dan

-- Alex Bennée