Re: [Qemu-devel] [PATCH v6 01/22] instrument: Add documentation

[Lluís Vilanova]

Lluís Vilanova writes:
[...]
> This was working on a much older version of instrumentation for QEMU, but I 
> can
> implement something that does the first use-case point above and some 
> filtering
> example (second use-case point) to see what's the performance difference.

Ok, so here's some numbers for the discussion (booting Emilio's ARM full system
image that immediately shuts down):

* Without instrumentation

  real  0m10,099s
  user  0m9,876s
  sys   0m0,128s

* Count number of memory access writes, by instrumenting only when they are
  executed

  real  0m15,896s
  user  0m15,752s
  sys   0m0,108s

* Counting same, but the filtering is done at translation time (i.e., not
  generate an execute-time callback if it's not a write)

  real  0m11,084s
  user  0m10,880s
  sys   0m0,112s

  As Peter said, the filtering can be added into the API to take advantage of
  this "speedup", without exposing translation vs execution time callbacks.

* Counting number of executed instructions, by instrumenting the beginning of
  each one of them

  real  0m24,583s
  user  0m24,352s
  sys   0m0,184s

* Counting same, but per-TB numbers are collected at translation-time, and we
  only generate a per-TB execution time callback to add the corresponding number
  of instructions for that TB

  real  0m11,151s
  user  0m10,952s
  sys   0m0,092s

  This really needs to expose translation vs execution time callbacks to take
  advantage of this "speedup".

Cheers,
  Lluis