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Update "Debugging Slow Builds" docs

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This updates the debugging slow builds docs to give more details about
what NINJA_SUMMARIZE_BUILD=1 does, and how to interpret the weighted
time numbers.

It also adds a mention of tools/buildstate.py, and updates the
instructions for finding build information on the bots.

Bug: None
Change-Id: I3eb6900012a577569c0e123e176221bf8889b768
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4766017
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1181532}
This commit is contained in:
Bruce Dawson
2023-08-09 16:48:03 +00:00
committed by Chromium LUCI CQ
parent 26811f52c2
commit d76e68103d
1 changed files with 16 additions and 2 deletions

18
build/docs/debugging_slow_builds.md

@ -10,8 +10,19 @@ cd out/Default
post_build_ninja_summary.py
```
Because the build is highly parallelized the `elapsed time` values are usually
not meaningful so the `weighted time` numbers are calculated to approximate
the impact of build steps on wall-clock time.
You can also set `NINJA_SUMMARIZE_BUILD=1` to have this command run
after each `autoninja` invocation (also runs ninja with `-d stats`).
after each `autoninja` invocation. Setting this environment variable also runs
ninja with `-d stats` which causes it to print out internal information such
as StartEdge times, which measures the times to create processes, and it
modifies the `NINJA_STATUS` environment variable to add information such as how
many processes are running at any given time - both are useful for detecting
slow process creation. You can get this last benefit on its own by setting
`NINJA_STATUS=[%r processes, %f/%t @ %o/s : %es ] ` (trailing space is
intentional).
To generate a Chrome trace of your most recent build:
@ -21,11 +32,14 @@ ninjatracing/ninjatracing out/Default/.ninja_log > trace.json
# Then open in https://ui.perfetto.dev/
```
If your build is stuck on a long-running build step you can see what it is by
running `tools/buildstate.py`.
## Slow Bot Builds
Our bots run `ninjatracing` and `post_build_ninja_summary.py` as well.
Find the trace at: `postprocess_for_goma > upload_log > ninja_log`:
Find the trace at: `postprocess for reclient > gsutil upload ninja_log > ninja_log`:
* _".ninja_log in table format (full)"_ is for `post_build_ninja_summary.py`.
* _"trace viewer (sort_by_end)"_ is for `ninjatracing`.