Re: [Qemu-devel] [PATCH v3 5/6] monitor: adding info tb and tbs to monitor

[Alex Bennée]

Markus Armbruster <address@hidden> writes:

> vandersonmr <address@hidden> writes:
>
<snip>

I'll leave Vanderson to address your other comments.

>
> Debugging commands are kind of borderline.  Debugging is commonly a
> human activity, where HMP is just fine.  However, humans create tools to
> assist with their activities, and then QMP is useful.  While I wouldn't
> encourage HMP-only for the debugging use case, I wouldn't veto it.
>
> Your (overly terse!) commit message and help texts make me guess the
> commands are for gathering statistics.  Statistics can have debugging
> uses.  But they often have non-debugging uses as well.  What use cases
> can you imagine for these commands?

So this is all really aimed at making TCG go faster - but before we can
make it go faster we need better tools for seeing where the time is
being spent and examining the code that we generate. So I expect the
main users of this functionality will be QEMU developers.

That said I can see a good rationale for supporting QMP because it is
more amenable to automation. However this is early days so I would
caution about exposing this stuff too early least we bake in a woolly
API.

The other wrinkle is we do have to take control of the emulator to
safely calculate some of the numbers we output. This essentially means
the HMP commands are asynchronous - we kick of safe work which waits
until all vCPU threads are stopped before we go through the records and
add up numbers. This is fine for the HMP because we just output to the
monitor FD when we are ready. I assume for QMP commands there is more
housekeeping to do? Can QMP commands wait for a response to be
calculated by another thread? Are there any existing commands that have
to support this sort of pattern?

>
> [...]


--
Alex Bennée