The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a7932f6f652d7a985d9bec588edf6349cf533d23

commit a7932f6f652d7a985d9bec588edf6349cf533d23
Author: jri <jri@chromium.org>
Date: Wed Jun 08 00:49:06 2016

Set FLAGS_shift_quic_cubic_epoch_when_app_limited to false.

R=rtenneti@chromium.org
BUG= 618144 

Review-Url: https://codereview.chromium.org/2050533002
Cr-Commit-Position: refs/heads/master@{#398441}

[modify] https://crrev.com/a7932f6f652d7a985d9bec588edf6349cf533d23/net/quic/quic_flags.cc

[Automated comment] Request affecting a post-stable build (M51), manual review required.

Your change meets the bar and is auto-approved for M52 (branch: 2743)

Before we approve merge to M51, Could you please confirm whether this change is baked/verified in Canary and safe to merge?

This flag has been in Canary since June 08 (5 days).

Please note that the bar is very high for post-stable M51. Do we need this in M51, what is the impact of this change and how safe is it?

This is a pretty severe bug, and it has caused serious problems for user uploads. The bug wasn't noticed until usage volume went up in M51. The fix is a single line of code that sets a flag to false -- we only need to turn off a flag to disable experimental code that is at the root of the bug, bringing behavior back to where it was without the experimental code.

jri@, can this be tested manually to verify it on Canary as per # 7.

Note: Please have the CL merged in to M52 branch so that it gets picked for Beta promotion scheduled on 06/15.

How long had this flag been turned on, in the stable channel? Any other possible side effects of disabling this flag?

I've verified manually that turning off the flag works as intended. The flag's been in Stable for a while, but was not supposed to be turned on, due to a known issue. Basically, the flag was a minor optimization to the algorithm that determines the sending rate of Chrome when using QUIC. Unfortunately, this code has a bug that causes the sending rate to spike dramatically, resulting in a large number of packet losses. 

Until M51, there was a cap on the sending rate that kept this bug hidden. M51 does not have that cap on sending rate, which exposes this bug. We run the same code at the GFEs (server-side of QUIC), and this flag has been off at the GFEs. We verified at the GFEs that turning the flag on increases sending rate dramatically, and we prompty turned it off at the GFEs. Unfortunately, we turned it on a while ago in Chrome and left it on.

I'm happy to meet in person or over vc to discuss this if that's easier.

Merge approved for M51 (branch 2704)

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

If all merges have been completed, please remove any remaining Merge-Approved labels from this issue.

Thanks for your time! To disable nags, add the Disable-Nags label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5bbce83225cc228294f08210e741dfd56a267839

commit 5bbce83225cc228294f08210e741dfd56a267839
Author: Eric Roman <eroman@chromium.org>
Date: Tue Jun 14 23:43:20 2016

Set FLAGS_shift_quic_cubic_epoch_when_app_limited to false.

R=rtenneti@chromium.org
BUG= 618144 

Review-Url: https://codereview.chromium.org/2050533002
Cr-Commit-Position: refs/heads/master@{#398441}
(cherry picked from commit a7932f6f652d7a985d9bec588edf6349cf533d23)

Review URL: https://codereview.chromium.org/2068043002 .

Cr-Commit-Position: refs/branch-heads/2704@{#719}
Cr-Branched-From: 6e53600def8f60d8c632fadc70d7c1939ccea347-refs/heads/master@{#386251}

[modify] https://crrev.com/5bbce83225cc228294f08210e741dfd56a267839/net/quic/quic_flags.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/303cfb7e56e845bf02dff2bd3b071e2f0633e6fe

commit 303cfb7e56e845bf02dff2bd3b071e2f0633e6fe
Author: Eric Roman <eroman@chromium.org>
Date: Tue Jun 14 23:36:57 2016

Set FLAGS_shift_quic_cubic_epoch_when_app_limited to false.

R=rtenneti@chromium.org
BUG= 618144 

Review-Url: https://codereview.chromium.org/2050533002
Cr-Commit-Position: refs/heads/master@{#398441}
(cherry picked from commit a7932f6f652d7a985d9bec588edf6349cf533d23)

Review URL: https://codereview.chromium.org/2069883003 .

Cr-Commit-Position: refs/branch-heads/2743@{#359}
Cr-Branched-From: 2b3ae3b8090361f8af5a611712fc1a5ab2de53cb-refs/heads/master@{#394939}

[modify] https://crrev.com/303cfb7e56e845bf02dff2bd3b071e2f0633e6fe/net/quic/quic_flags.cc