On Mon, Jun 10, 2013 at 07:38:34PM +0300, Gleb Natapov wrote: > > Guest traces contain vcpu number and not pid (because guest is unaware > > of host PID). > > > No, guest trace is just a regular ftrace done inside a guest. It contains > guest's PIDs which is useless for host.
# tracer: nop # # entries-in-buffer/entries-written: 5333/5333 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | Traces contain CPU ID. > I do not know how exactly guest traces are transfered to a host, if > each vcpu buffer is transfered separately host can figure out what > trace entry belong to which vcpu based on what buffer the trace is in. > But the information about what buffer belongs to which vcpu id should > be transfered to a host somehow too. > > > > > However, when we > > > > focus on output data of the write_tsc_offset event, it is difficult to > > > > directly understand contents of the data if vcpu number information is > > > > not included. So, including the information is useful, I think. > > > > > > > How your tool does it now? > > > > It merges guest trace with host trace (by converting the TSC timestamp > > in the guest trace to host TSC using tsc_offset information). > > > I mean how it does it now without vcpu id. The answer is that it works > for only one vcpu now. Yes. > > By not recording vcpu ID in the tsc_offset trace, it is necessary to > > supply the tool with PID<->VCPU_id tuples for translation (so its an > > additional step required, and it makes trace merge impossible > > if the information is not available). > The tool needs PID<->VCPU_id tuples to do the merging of any trace > entry. Without that it does not know how to interpret entry timestamps > (which offset to use). Apparently it will get this information from > vmentry trace point. What is so special about tsc_offset tracing that > it needs to contain vcpuid by itself. If the tsc_offset tracepoint contains vcpu ID, its possible to lookup guest trace entry (which contains CPU ID), and match on that. Without that, PID<->VCPU_id tuples are necessary. Yes? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
