All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=756623

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=34ae514d506c68daa5a2b1afaca738a33ed846f08d6b8102d008ef8fa3f5b465


Bot(s) for this bug's original alert(s):

chromium-rel-mac11

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/8970977415960603072

Bisect cannot reproduce with confidence. Will try a wider range.

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/8970911202877090208

=== BISECT JOB RESULTS ===
Perf regression found with culprit

Suspected Commit
  Author : Greg Kerr
  Commit : 9705b7aaabf4c81d4e9cb13174338df9bde61cc4
  Date   : Tue Aug 15 19:42:42 2017
  Subject: Enable Finch Trial Test for MacV2Sandbox.

Bisect Details
  Configuration: mac_10_11_perf_bisect
  Benchmark    : loading.desktop
  Metric       : timeToFirstMeaningfulPaint_avg/pcv1-cold/Chosun
  Change       : 12.40% | 761.876222221 -> 856.323999999

Revision             Result                  N
chromium@494278      761.876 +- 122.812      9       good
chromium@494469      785.713 +- 65.5089      9       good
chromium@494493      801.96 +- 167.016       14      good
chromium@494499      791.424 +- 106.276      14      good
chromium@494501      793.848 +- 89.6817      9       good
chromium@494502      862.699 +- 515.202      21      bad       <--
chromium@494506      847.393 +- 134.838      14      bad
chromium@494517      834.506 +- 116.378      14      bad
chromium@494565      836.747 +- 151.052      9       bad
chromium@494660      856.324 +- 135.348      9       bad

To Run This Test
  src/tools/perf/run_benchmark -v --browser=release --output-format=chartjson --upload-results --pageset-repeat=1 --also-run-disabled-tests --story-filter=Chosun loading.desktop

More information on addressing performance regressions:
  http://g.co/ChromePerformanceRegressions

Debug information about this bisect:
  https://chromeperf.appspot.com/buildbucket_job_status/8970911202877090208


For feedback, file a bug with component Speed>Bisection

This is a different test failing than 756145, so why was this duped? 756145 is Fixed, is this issue fixed as well?

It looks like the merge was done by automated tooling, so I am un-duplicating this bug. 

Upgraded to P-1, we can't ship with this regression.

Running a perf try job to find out if this is caused by the extra execv() happening when a process is launched now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/66d4a01a3d80c6cb507112d230824d1e9cdafee7

commit 66d4a01a3d80c6cb507112d230824d1e9cdafee7
Author: Greg Kerr <kerrnel@chromium.org>
Date: Mon Aug 21 22:45:05 2017

Mac V2 Sandbox: Disable re-execution of helper executable.

To address a performance regression in startup times, the Helper
executable will no longer re-execute itself after the sandbox is
engaged.

Bug:  756623 
Change-Id: I36dd44b222eae10e2ac17574ebc70588fdebf592
Reviewed-on: https://chromium-review.googlesource.com/624378
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Greg Kerr <kerrnel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496100}
[modify] https://crrev.com/66d4a01a3d80c6cb507112d230824d1e9cdafee7/chrome/app/OWNERS
[modify] https://crrev.com/66d4a01a3d80c6cb507112d230824d1e9cdafee7/chrome/app/chrome_exe_main_mac.cc

chiniforooshan@chromium.org, where do I look to see if this perf regression has returned to baseline? Thanks.

The link to the main alert is

https://chromeperf.appspot.com/group_report?sid=34ae514d506c68daa5a2b1afaca738a33ed846f08d6b8102d008ef8fa3f5b465

It looks like the commit in #10 did NOT bring the metric back down.

That is surprising. Do you have any advice on how to drill into where the additional time is being spent in this case? I can just revert the original commit and (hopefully) restore the metric, but I would like to understand the root cause first.

Note that this is a finch trial, so the regression isn't affecting actual customer builds.

+Kouhei and Kunihiko, the benchmark owners, for benchmark specific suggestions.

Generally, I would try to reproduce the regression by running the benchmark locally for faster debugging cycle. Also, you can check if you see anything suspicious in the trace. Here is the link to a trace after the regression (open it with your @google account):

https://console.developers.google.com/m/cloudstorage/b/chrome-telemetry-output/o/trace-file-id_73-2017-08-15_11-25-14-28677.html

And one before the regression:
https://console.developers.google.com/m/cloudstorage/b/chrome-telemetry-output/o/trace-file-id_73-2017-08-15_03-43-45-82877.html

I struggle to debug the benchmarks locally because they're very noisy when
run locally. So I can't get a solid "base" time for the benchmark, which
makes it impractical to debug since the executions times are all over the
place, both before and after the suspect commit.

Is this regression only being since on 10.11 or is that just the macOS version the bisect ran on? Knowing the exact macOS version will really help me to diagnose this.

The original bug was filed about Mac 10.11 regressions. I took a look, and there are some alerts in the same range on Mac 10.12. It's not clear if they have the same root cause; I filed  bug 757993  to bisect.

 Issue 758199  has been merged into this issue.

I'll look at all the data again, but it probably makes sense for me to do a revert at this point to see if the metrics calm down.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4fa660ddcdc1744e5f4380c336df5c8e2226642c

commit 4fa660ddcdc1744e5f4380c336df5c8e2226642c
Author: Greg Kerr <kerrnel@chromium.org>
Date: Thu Aug 24 20:48:27 2017

Revert "Enable Finch Trial Test for MacV2Sandbox."

This reverts commit 9705b7aaabf4c81d4e9cb13174338df9bde61cc4.

Reason for revert: This CL seems to be causing performance regressions.
 crbug.com/757993 

Original change's description:
> Enable Finch Trial Test for MacV2Sandbox.
>
> Cq-depend: CL:611386
> Bug: 749839
> Change-Id: I03057065380f5e49b899f1c9f9869e175d3223dc
> Reviewed-on: https://chromium-review.googlesource.com/612323
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: Steven Holte <holte@chromium.org>
> Commit-Queue: Greg Kerr <kerrnel@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#494502}

TBR=rsesek@chromium.org,holte@chromium.org

Bug:  756145 , 756623 
Change-Id: Iccada6b649f20f07ea4af4fdc995dc1a8426ded4
Reviewed-on: https://chromium-review.googlesource.com/633623
Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Greg Kerr <kerrnel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497180}
[modify] https://crrev.com/4fa660ddcdc1744e5f4380c336df5c8e2226642c/testing/variations/fieldtrial_testing_config.json