e10s must not cause the slow-script dialog to appear more often. A/B testing on beta should indicate that the slow script dialog appears no more often than before.

RASCI

• Responsible: azhang
• Accountable: bsmedberg
• Supporting:
• Consulted:
• Informed: cpeterson, elan, release management

Metrics

SLOW_SCRIPT_PAGE_COUNT

Summary:

• SLOW_SCRIPT_PAGE_COUNT made it into beta46, and we've obtained data for it in the beta46-noapz and beta46-apz experiment.
• See the latest beta46-apz experiment analysis: SLOW_SCRIPT_PAGE_COUNT still shows slightly more often on e10s than non-e10s, but the difference is much smaller than with SLOW_SCRIPT_NOTICE_COUNT.
• We've verified that SLOW_SCRIPT_PAGE_COUNT measures the same thing across e10s and non-e10s.

Relevant info from beta46-apz slow script analysis:

Median difference in payload/histograms/SLOW_SCRIPT_PAGE_COUNT per hour is 0.12, (0.47, 0.35). The probability of this effect being purely by chance is 0.00.

Technical details:

• SLOW_SCRIPT_PAGE_COUNT is essentially a version of SLOW_SCRIPT_NOTICE_COUNT that can be compared between e10s and non-e10s. It counts only the first slow script notice per page, which accounts for the difference in notice behaviours.
• There should be no differences in the slow script reporting mechanism between e10s and non-e10s; 1 call to ShowSlowScriptDialog means 1 addition to the histogram regardless of e10s setting. Manual testing supports this.
• The timeout has changed from 2 to 10 in e10s builds (see https://hg.mozilla.org/mozilla-central/rev/63680efe6d55#l35.12 for before and https://hg.mozilla.org/mozilla-central/rev/5002e9c06365#l2.13 for after). However, the value is correct on all beta versions, from 45.0b1 to 45.0b8 - this does not affect our measurements.
•  :azhang has verified that beta 46 releases with/without e10s both increment SLOW_SCRIPT_PAGE_COUNT and SLOW_SCRIPT_NOTICE_COUNT if and only if there is a slow script notification shown, and that they seem to have the exact same timeout in all cases.

Links:

• bug 1251667 - [e10s] Add new telemetry probe to count pages with one or more slow script notes (SLOW_SCRIPT_PAGE_COUNT?)
• https://github.com/vitillo/e10s_analyses/blob/master/beta46-apz/e10s_experiment.ipynb - e10s-beta46-apz experiment main analysis, (this has a section for slow scripts).
• https://github.com/vitillo/e10s_analyses/blob/master/beta46-noapz/e10s_experiment.ipynb - e10s-beta46-noapz experiment main analysis, (this has a section for slow scripts).
• https://gist.github.com/Uberi/64be9b7946849fa45e50 - slow script analysis
• bug 1249845 - tracking bug for the beta46-apz experiment
• bug 1253669 - tracking bug for the beta46-noapz experiment
• bug 1249978 - [e10s] SLOW_SCRIPT_NOTICE_COUNT regressed in beta experiment
• bug 1182638 - [e10s][telemetry] slow-script dialog appears twice as often in e10s vs non-e10s

Analysis results: SLOW_SCRIPT_PAGE_COUNT shows up slightly more often in e10s. Analysis was reviewed by: rvitillo

How slow script notice count works on non-e10s:

• nsGlobalWindow::ShowSlowScriptDialog accumulates the SLOW_SCRIPT_NOTICE_COUNT histogram (https://dxr.mozilla.org/mozilla-central/source/dom/base/nsGlobalWindow.cpp#10677)

How slow script notice count works on e10s:

• [CHILD] nsGlobalWindow::ShowSlowScriptDialog sends a slow script notification via ProcessHangMonitor::NotifySlowScript (https://dxr.mozilla.org/mozilla-central/source/dom/base/nsGlobalWindow.cpp#10652)
• [CHILD] HangMonitorChild::NotifySlowScript invokes HangMonitorChild::NotifySlowScriptAsync to send out the slow script notice (https://dxr.mozilla.org/mozilla-central/source/dom/ipc/ProcessHangMonitor.cpp#352)
• [CHILD] PProcessHangMonitorChild::SendHangEvidence invokes PProcessHangMonitorParent::OnMessageReceived via IPC (https://dxr.mozilla.org/mozilla-central/source/obj-x86_64-unknown-linux-gnu/ipc/ipdl/PProcessHangMonitorChild.cpp#108)
• [PARENT] HangMonitorParent::RecvHangEvidence is called when PProcessHangMonitorParent receives a message from the child process (https://dxr.mozilla.org/mozilla-central/source/obj-x86_64-unknown-linux-gnu/ipc/ipdl/PProcessHangMonitorParent.cpp#288)
• [PARENT] HangMonitorParent::RecvHangEvidence sends out a "process-hang-report" event by creating a HangObserverNotifier task (https://dxr.mozilla.org/mozilla-central/source/dom/ipc/ProcessHangMonitor.cpp#610)
• [PARENT] ProcessHangMonitor.reportHang is called when the ProcessHangMonitor receives a "process-hang-report" event (https://dxr.mozilla.org/mozilla-central/source/browser/modules/ProcessHangMonitor.jsm#66)
• [PARENT] JS function ProcessHangMonitor.reportHang accumulates the SLOW_SCRIPT_NOTICE_COUNT histogram (https://dxr.mozilla.org/mozilla-central/source/browser/modules/ProcessHangMonitor.jsm#403)
•  :azhang checked that this is currently the only code path that results in SLOW_SCRIPT_NOTICE_COUNT being incremented.

Bugs

1 Total; 1 Open (100%); 0 Resolved (0%); 0 Verified (0%);