All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=818627

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=98997a50bc134b159797cbec535c5924f0d24ff66a2baf0ac236ac142dc47aba


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

android-nexus5
android-nexus5X
android-nexus6
android-nexus7v2

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/14cc175c440000

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/14cc175c440000

Reland "[parser] Remove pretenuring of closures assigned to properties" by adamk@chromium.org
https://chromium.googlesource.com/v8/v8/+/3d7ad2e7e53d3cd6add51512580c054abf7e5805

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

Apparently this wasn't seen the first time we landed the removal of pretenuring. In fact I don't see the spike from that first landing, which makes me wonder if some intervening change is part of the cause here.

This looks really odd. Do you know that these benchmarks are about?

"key_silk_cases" are generally about smooth animation/scrolling. And the metric here, "thread_other_cpu_time_per_frame", does suggest that something's getting in the way (my guess would be some GC work). rmcilroy, do you have more detailed background?

I don't have any more details, what you describe sounds right to me. Adding ajuma@ who is listed as the benchmark owner in case they can provide any better background.

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/16d9e8ca440000

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/11b24e62440000

Don't have much more to add -- these tests measure cpu time for various threads. It's a bit surprising to me though that a V8 change would affect cpu time for raster worker threads or the browser, so I've triggered bisects on those changes.

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/16d9e8ca440000

Reland "[parser] Remove pretenuring of closures assigned to properties" by adamk@chromium.org
https://chromium.googlesource.com/v8/v8/+/3d7ad2e7e53d3cd6add51512580c054abf7e5805

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/11b24e62440000

Reland "[parser] Remove pretenuring of closures assigned to properties" by adamk@chromium.org
https://chromium.googlesource.com/v8/v8/+/3d7ad2e7e53d3cd6add51512580c054abf7e5805

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

My stab-in-the-dark guess is that if we look at a trace of this benchmark on a device, we'll see the V8 GC doing a bunch of work that's interfering with the ability of other browser/raster work to get scheduled by the OS.

adamk@: perf bots produce trace and you can access them from perf dashboard. You may
also request the bot to produce a more detailed trace with desired categories.


Here is for example the default trace for one of the worst regressions: https://console.developers.google.com/m/cloudstorage/b/chrome-telemetry-output/o/http___mobile_news_sandbox_google_com_news_pt0_swipe_2018-03-03_02-30-08_19078.html

I am not sure what to look for but you may be able to test your hypothesis.

I ran a job (https://pinpoint-dot-chromeperf.appspot.com/job/14e62931440000) with some v8-specific tracing bits, but my trace-reading skills around non-renderer stuff are not sharp.

Bizarrely, this metric seems to have gone to 0 after https://chromium.googlesource.com/chromium/src/+log/b73107cb0226c61a1afae2457f2a3988c1b18c0b..2a7c3b2cd5c6ad903ae422d5e6ce45a123ab92ac. ajuma, does something in that commit log look like it could've caused this?

Nothing obvious. I've filed  bug 823315  for bisecting that range.

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/5cf2ae5a4d7224198a0474eb27cc618b6843bc32

commit 5cf2ae5a4d7224198a0474eb27cc618b6843bc32
Author: Adam Klein <adamk@chromium.org>
Date: Mon Mar 26 19:09:22 2018

Revert "Reland "[parser] Remove pretenuring of closures assigned to properties""

This reverts commit 3d7ad2e7e53d3cd6add51512580c054abf7e5805.

Reason for revert: too many regressions to handle for now.

Original change's description:
> Reland "[parser] Remove pretenuring of closures assigned to properties"
>
> The memory gains were significant, so despite the bluebird-doxbee
> regression, we think it's better to have this patch than not.
> See the attached Chromium bug for more discussion.
>
> This is a reland of 20e346bd08591caff2f7c45de762ca4d4e3f72c8.
>
> Original change's description:
> > [parser] Remove pretenuring of closures assigned to properties
> >
> > This pretenuring was added in https://codereview.chromium.org/5220007,
> > back when it was necessary in order to allow use of the closure
> > as a "constant function" property. This should no longer be the case,
> > and the pretenuring causes some unfortunate downstream effects.
> >
> > This patch removes the parser's setting of this bit. If it doesn't
> > cause regressions on the perf bots, followup CLs will remove the
> > rest of the support for this feature.
> >
> > Bug:  v8:7442 
> > Change-Id: I27c43dd4293ce5de921be6c78571e712778d138a
> > Reviewed-on: https://chromium-review.googlesource.com/914610
> > Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> > Commit-Queue: Adam Klein <adamk@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#51254}
>
> Bug:  v8:7442 ,  chromium:814182 
> Change-Id: I228c59dccef3844803f115749e72ae6c5f286eda
> Reviewed-on: https://chromium-review.googlesource.com/938241
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Commit-Queue: Adam Klein <adamk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51668}

Tbr: gsathya@chromium.org
Bug:  v8:7442 ,  v8:7524 ,  chromium:814182 ,  chromium:818627 ,  chromium:818672 ,  chromium:819994 ,  chromium:821788 
Change-Id: Ib760d63f879613f3b874889c5cb29ba2a77ba430
Reviewed-on: https://chromium-review.googlesource.com/980795
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52233}
[modify] https://crrev.com/5cf2ae5a4d7224198a0474eb27cc618b6843bc32/src/parsing/parser-base.h
[modify] https://crrev.com/5cf2ae5a4d7224198a0474eb27cc618b6843bc32/src/parsing/parser.h
[modify] https://crrev.com/5cf2ae5a4d7224198a0474eb27cc618b6843bc32/src/parsing/preparser.h