On Thu, Jul 13, 2017 at 04:01:09PM +0800, Wang Dong wrote: > On 07/10/2017 08:40 PM, Stefan Hajnoczi wrote: > > 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 > > I thought the example in doc was enabled by default. > > Thanks for your reply. Below is my command: > When to compile: > > ./configure --enable-debug --enable-trace-backends=simple > > $ echo bdrv_aio_readv > /tmp/events > $ echo bdrv_aio_writev >> /tmp/events > > > qemu [...] > > -chardev socket,id=mon1,host=localhost,port=7777,server,nowait \ > -mon chardev=mon1,mode=control,pretty=on \ > -trace events=/tmp/events > > > Did I miss something?
Recent QEMU versions do not have bdrv_aio_readv/bdrv_aio_writev trace events, so you may not get any output. Which events do you actually want to trace? I will update the example in docs/devel/tracing.txt with trace events that are more likely to be triggered. Stefan
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