[Qemu-devel] trace: timestamps, core IDs, and file creation

[Hollis Blanchard <hollis_blanchard@mentor.com>]

Hi Stefan, I've been starting to use qemu tracing and found it quite 
useful. I have a couple comments about the trace events in general:

The event timestamps are host time (get_clock()). I'm correlating qemu 
events with other logs (using icount), so host time is unhelpful. Could 
we use cpu_get_clock() instead? (Trace events are used in other tools 
like qemu-io, where guest time doesn't exist, and there we could 
continue to use get_clock().)

When trying to understand multi-core guest behavior, it's pretty 
important to know which core is performing the traced action (e.g. 
MMIO). Would it make sense to automatically embed the core index, like 
the timestamp, or do you think it should be encoded in each individual 
tracepoint?

Right now, the simple tracepoint backend creates a trace file even when 
no events are active and no -trace options are present. Compounding the 
situation, omitting "-trace file=foo" results in the directory being 
littered with trace-NNNN files... could we create the file only when 
tracing is activated? And maybe with a more predictable name?

-- 
Hollis Blanchard
Mentor Graphics Emulation Division