Re: [Qemu-devel] [PATCH v7 0/7] trace: [tcg] Optimize per-vCPU tracing states with separate TB caches

[Lluís Vilanova]

Emilio G Cota writes:

> On Fri, Jan 13, 2017 at 21:48:09 +0100, Lluís Vilanova wrote:
> (snip)
>> To handle both issues, this series integrates the dynamic tracing event state
>> into the TB hashing function, so that vCPUs tracing different events will use
>> separate TBs. Note that only events with the 'vcpu' property are used for
>> hashing (as stored in the bitmap of CPUState->trace_dstate).

> Is this going to be picked up by anyone? AFAICT the patchset is close
> to being merge-ready.

> Lluís: I'm very interested in your instrumentation work [1]:

> - How much up to date are the branches in [1]? I couldn't find this
>   v7 iteration in there, although maybe I didn't look carefully enough.

> - Are you planning on upstreaming it? I have some time to help with
>   that if you're interested.

After your latest re-spin on this series, there's two basic pieces missing
upstream to have instrumentation:

* An interface to insert user callbacks on events.

* A useful mechanism to pass value place holders (values are later calculated)
  to these callbacks. This is useful when instrumenting an event before it
  happens (e.g., before an instruction is executed) to pass it some values that
  are only known afterwards (e.g., number of instructions in a BBL). I called
  them promises, and you can see an example in [2] (using an older API of QDBI).


> - Do you have instrumentation examples beyond what's in
>   docs/instrumentation.txt? In particular I'd like to see how the basic
>   block (BBL) instrumentation works, i.e. how a 'skeleton' simulator
>   would work to decode the guest instructions and also track their
>   dependences.

No, sorry, I never got around to writing such type of instrumentation
example. The closest I have is [2].


[2] https://projects.gso.ac.upc.edu/projects/qdbi-simpoint


> Thanks,

>               Emilio

> [1] https://projects.gso.ac.upc.edu/projects/qemu-dbi


Cheers,
  Lluis