On Tue, Jun 20, 2017 at 10:12:14PM +0530, Prasun Ratn wrote: > I am trying to get qemu events using ftrace but not seeing any events in the > ftrace logs. I see kvm logs like the following but no qemu events such as virtio > blk events. I'm using a locally compiled qemu version with ftrace > backend enabled. > > [001] d... 9290.926939: kvm_exit: reason HLT rip 0xffffffff81058e95 info 0 0 > > This is how I am enabling ftrace logs: > > echo 1 >/sys/kernel/debug/tracing/events/kvm/enable > echo 1 > /sys/kernel/debug/tracing/tracing_on > > # run cmd > $CMD Please post the command-line. You need to enable the events you are interested in. Either use the -trace option or via the HMP monitor (trace-event NAME on|off)/QMP monitor (trace-event-set-state). > > # disable trace > echo 0 >/sys/kernel/debug/tracing/events/kvm/enable > echo 0 > /sys/kernel/debug/tracing/tracing_on > > # copy trace > echo Copying trace to $outfile > cp /sys/kernel/debug/tracing/trace $outfile > > To debug, I build qemu with the 'log' backend, and I am able to see the > appropriate events in /var/log/libvirt log files. > > However if I rebuild qemu with ftrace backend, I don't see any events. Do I need > to enable any other tracing events in /sys/kernel/debug/tracing? Do I need to > run any qemu monitor cmds? > > Any thing obvious I may be missing? Any debug steps recommended? Did you strace -f QEMU to see if there are writes to the trace_marker file? If you see the write() syscalls then you need to double-check your commands to set up and access /sys/kernel/debug/tracing. If you do not see the write() syscalls then you need to check that you build QEMU with the ftrace backend and enabled the trace events you are interested in.
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