Add experiment for background tracing init [chromium/src : main]
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Peter Birk Pakkenberg (Gerrit)
Feb 2, 2026, 9:40:24 AM (5 days ago) Feb 2
to Richard (Torne) Coles, Abhijith Nair, Chromium LUCI CQ, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
Attention needed from Abhijith Nair and Richard (Torne) Coles
Peter Birk Pakkenberg added 1 comment![]( "Open in Gerrit")
File android_webview/browser/aw_browser_process.cc
Line 402, Patchset 4:
if (g_initializing_perfetto_on_background_thread) {Richard (Torne) Coles . resolved
Peter Birk PakkenbergIf the call to InitPerfetto has been posted to a background thread then I don't think anything guarantees that it will have reached the point of setting this variable to true before this function is called?
I think you would need to always signal the event and always wait on it, and only read `g_initializing_perfetto_on_background_thread` *after* successfully waiting for it if you want to know whether it was done on the background thread or not for the purposes of the metric.
Agreed, good catch.
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Peter Birk Pakkenberg (Gerrit)
Feb 2, 2026, 10:48:00 AM (5 days ago) Feb 2
to Nate Fischer, Richard (Torne) Coles, Abhijith Nair, Chromium LUCI CQ, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
Attention needed from Abhijith Nair, Nate Fischer and Richard (Torne) Coles
Peter Birk Pakkenberg added 2 comments![]( "Open in Gerrit")
Patchset-level comments
File-level comment, Patchset 8 (Latest):
Peter Birk Pakkenberg . resolved
Hi Nate, do you have capacity to review this while Torne is OOO?
File android_webview/browser/aw_browser_process.cc
Line 402, Patchset 4:
if (g_initializing_perfetto_on_background_thread) {Richard (Torne) Coles . resolved
Peter Birk PakkenbergIf the call to InitPerfetto has been posted to a background thread then I don't think anything guarantees that it will have reached the point of setting this variable to true before this function is called?
I think you would need to always signal the event and always wait on it, and only read `g_initializing_perfetto_on_background_thread` *after* successfully waiting for it if you want to know whether it was done on the background thread or not for the purposes of the metric.
Agreed, good catch.
Peter Birk Pakkenberg
I've moved the update to the global flag to the main thread instead, to ensure that we only wait when we did initialize on a background thread. Otherwise we would have a situation where the current flow would wait indefinitely because InitTracing isn't called in the baseline implementation.
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Nate Fischer (Gerrit)
Feb 3, 2026, 7:21:22 PM (4 days ago) Feb 3
to Peter Birk Pakkenberg, Peter Beverloo, Richard (Torne) Coles, Abhijith Nair, Chromium LUCI CQ, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
Attention needed from Abhijith Nair, Peter Beverloo, Peter Birk Pakkenberg and Richard (Torne) Coles
Nate Fischer voted Code-Review+1![]( "Open in Gerrit")
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Peter Birk Pakkenberg (Gerrit)
Feb 4, 2026, 4:56:06 AM (3 days ago) Feb 4
to Colin Blundell, Nate Fischer, Peter Beverloo, Richard (Torne) Coles, Abhijith Nair, Chromium LUCI CQ, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
Attention needed from Abhijith Nair, Colin Blundell, Peter Beverloo and Richard (Torne) Coles
Peter Birk Pakkenberg voted and added 1 comment![]( "Open in Gerrit")
Votes added by Peter Birk Pakkenberg
| Auto-Submit | +1 |
| Commit-Queue | +1 |
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Patchset-level comments
Peter Birk Pakkenberg . resolved
Colin would you mind doing an OWNERS review of //services/tracing on this CL (2 files). I am adding timing histograms to the initialization process to help improve WebView startup times.
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Colin Blundell (Gerrit)
Feb 4, 2026, 4:57:01 AM (3 days ago) Feb 4
to Peter Birk Pakkenberg, Colin Blundell, Nate Fischer, Peter Beverloo, Richard (Torne) Coles, Abhijith Nair, Chromium LUCI CQ, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
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| Code-Review | +1 |
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Peter Beverloo (Gerrit)
Feb 4, 2026, 7:47:44 AM (3 days ago) Feb 4
to Peter Birk Pakkenberg, Peter Beverloo, Colin Blundell, Nate Fischer, Richard (Torne) Coles, Abhijith Nair, Chromium LUCI CQ, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
Attention needed from Abhijith Nair, Colin Blundell, Peter Birk Pakkenberg and Richard (Torne) Coles
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Chromium LUCI CQ (Gerrit)
Feb 4, 2026, 7:53:14 AM (3 days ago) Feb 4
to Peter Birk Pakkenberg, Peter Beverloo, Colin Blundell, Nate Fischer, Richard (Torne) Coles, Abhijith Nair, AyeAye, Chromium Metrics Reviews, chromium...@chromium.org, tracing...@chromium.org, spang...@chromium.org, wfh+...@chromium.org, android-web...@chromium.org, asvitkine...@chromium.org
Chromium LUCI CQ submitted the change![]( "Open in Gerrit")
Change information
Commit message:
Add experiment for background tracing init
This experiment posts the initialization of the tracing service and
Perfetto to a background task runner as soon as the native library has
been initialized, and ensures that startup waits for the task to finish
before continuing.
Bug: 480077118
Change-Id: Iaf8af4ddb6e182b81af56ad1880beb023f5fb72a
Commit-Queue: Peter Beverloo <pe...@chromium.org>
Reviewed-by: Nate Fischer <ntf...@chromium.org>
Reviewed-by: Colin Blundell <blun...@chromium.org>
Reviewed-by: Peter Beverloo <pe...@chromium.org>
Auto-Submit: Peter Birk Pakkenberg <pb...@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1579365}
Files:
- M android_webview/browser/aw_browser_process.cc
- M android_webview/browser/aw_browser_process.h
- M android_webview/common/aw_feature_map.cc
- M android_webview/common/aw_features.cc
- M android_webview/common/aw_features.h
- M android_webview/glue/java/src/com/android/webview/chromium/WebViewChromiumFactoryProvider.java
- M android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java
- M android_webview/java/src/org/chromium/android_webview/common/ProductionSupportedFlagList.java
- M android_webview/java/src/org/chromium/android_webview/common/WebViewCachedFlags.java
- M android_webview/lib/aw_main_delegate.cc
- M services/tracing/public/cpp/perfetto/perfetto_traced_process.cc
- M services/tracing/public/cpp/trace_startup.cc
- M testing/variations/fieldtrial_testing_config.json
- M tools/metrics/histograms/metadata/android/histograms.xml
- M tools/metrics/histograms/metadata/others/histograms.xml
Change size: M
Delta: 15 files changed, 213 insertions(+), 30 deletions(-)
Branch: refs/heads/main
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Code-Review: +1 by Colin Blundell, +1 by Nate Fischer, +1 by Peter Beverloo
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