plugin: measure max/avg latencies of all plugin API

A simple stat collecting. Uses RAII to gather latency on all exit
paths from function/block. The underscore in "let _u = STATS.u(...)" is
to pacify "unused variable" warning. Using "let _ = " makes compiler
optimize out the call.

Rust makes it particularly hard to convert enums from integers, so I had
to add a hack that stores Enum on every invocation of the STATS.u. Looking
at disassembly, it added one move of constant to the field of STATS.entries;
no heap operations or cloning. A clever alternative using macros was
suggested by semenzato@, but I decided saving an instruction was not
worth the complexity.

The output is currently printed on the destruction of crosvm, so tests
print out stats on exit. We probably should find a better place for it
though.

BUG=None
TEST=cargo test --release --features plugin

Change-Id: I78a8920e9896b717af3aaea14f8ed6013be6b94f
Reviewed-on: https://chromium-review.googlesource.com/1036473
Commit-Ready: Slava Malyugin <slavamn@chromium.org>
Tested-by: Slava Malyugin <slavamn@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>

0 files changed, 0 insertions, 0 deletions