Re: [Qemu-devel] About the trace framework

[Stefan Hajnoczi]

On Mon, Jul 10, 2017 at 01:24:23PM +0800, Xie Changlong wrote:
> 在 7/9/2017 5:57 PM, Wang Dong 写道:
> > Hi,
> > 
> > I am new to QEMU. But I got some problem so that  I want to figure it out.
> > 
> > So I try to debug qemu to see what happened.
> > 
> > And I found trace framework. I think this will help me understand the
> > point.
> > 
> > So I compiled qemu with option:
> > 
> > ## *--enable-trace-backends=simple*
> > 
> > And did as the docs/tracing.txt tell. But when I execute the example
> > command in it, nothing just happens.
> > 
> > *./scripts/simpletrace.py trace-events-all trace-xxxxxx(my trace file
> > produced by qemu)
> > I am not sure what happened. Just ask this.
> > Any clue will be appreciated. Thanks in advance.
> > *
> > 
> 
> Did you set *trace-event*? I've encountered this issue in the past :)
> (qemu) help trace-event
> trace-event name on|off -- changes status of a specific trace event
> (qemu) info trace-events

Yes, you need to enable specific trace events that you are interested
in.  'trace-event' does that from the QEMU monitor at runtime.  If you'd
rather keep a file with a list of events to enable:

  $ echo bdrv_aio_readv   > /tmp/events
  $ echo bdrv_aio_writev >> /tmp/events
  $ qemu -trace events=/tmp/events ... # your normal QEMU invocation

It's hard to know what is missing without seeing your QEMU command-line
and monitor commands you used.

Stefan

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