Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected) [bug 12465]

Kevin Shanahan
2009-02-22T10:39:14Z

On Sun, 2009-02-15 at 11:04 +0100, Ingo Molnar wrote:
> qemu-sy-4237 has been scheduled away, and the system appeared to have done
> nothing in the meantime. That's not something that really looks like a
> scheduler regression - there is nothing the scheduler can do if KVM
> decides to block a task.
>
> It would be nice to enhance this single-CPU trace some more - to more
> surgically see what is going on. Firstly, absolute timestamps would be
> nice:
>
> echo funcgraph-abstime > trace_options
> echo funcgraph-proc > trace_options
>
> as it's a bit hard to see the global timescale of events.

I was going to try and grab the trace with absolute timestamps tonight,
but that option doesn't seem to be available in Linus' current kernel.

flexo:/sys/kernel/debug/tracing# echo 0 > tracing_enabled
flexo:/sys/kernel/debug/tracing# echo function_graph > current_tracer
flexo:/sys/kernel/debug/tracing# echo funcgraph-proc > trace_options
flexo:/sys/kernel/debug/tracing# echo funcgraph-abstime > trace_options
-su: echo: write error: Invalid argument
flexo:/sys/kernel/debug/tracing# cat trace_options
print-parent nosym-offset nosym-addr noverbose noraw nohex nobin noblock
nostacktrace nosched-tree ftrace_printk noftrace_preempt nobranch
annotate nouserstacktrace nosym-userobj noprintk-msg-only
nofuncgraph-overrun funcgraph-cpu funcgraph-overhead funcgraph-proc
flexo:/sys/kernel/debug/tracing# uname -a
Linux flexo 2.6.29-rc5-00299-gadfafef #6 SMP Sun Feb 22 20:09:37 CST
2009 x86_64 GNU/Linux

What am I missing?

Cheers,
Kevin.