Re: [Qemu-devel] [PATCH v4 00/20] instrument: Add basic event instrumentation

[Lluís Vilanova]

Emilio G Cota writes:

> On Wed, Sep 06, 2017 at 20:22:41 +0300, Lluís Vilanova wrote:
>> This series adds an API to add instrumentation events.
>> 
>> It also provides additional APIs for:
>> * Controlling tracing events

> hmm didn't Stefan say that tracing should be decoupled from this?

I understood decoupling instr from the tracing infrastructure (since tracing
events are defined as not stable, and instr must be stable by definition).


>> * Peek/poke guest memory
>> 
>> There's still missing APIs for (can be added in later series?):
>> * Provide something like tracing's per-vCPU trace states (i.e., so that each
>> vCPU can have different instrumentation code). It's still not clear to me if
>> we should extend the per-vCPU bitmap with instrumentation events, or 
>> otherwise
>> somehow reuse the bits in tracing events (since they're currently limited).

> As I said in the description of my alternative implementation [*], I don't see
> much value in having per-vCPU events, as most instrumenters just care about
> the guest application/system. I can only think of cases where the instrumenter
> is only interested in a guest process (in system-mode), but that'd be ugly
> anyway (would need to change both QEMU and the guest kernel to track the pid).

> If the need ever arises, we could add __vcpu(cpu_index) registration 
> functions.

> [*] https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg01446.html

Sorry, your series slipped my radar. I'll take a look at it.


Thanks,
  Lluis