[APPLIED] [RFC] [Maverick] Enable CONFIG_TASK_DELAY_ACCT=y

[Leann Ogasawara]

Applied to Maverick linux master.

Thanks,
Leann

>From 8b2da9d17c8b1b7ae64f7f9cd57ec373e7494644 Mon Sep 17 00:00:00 2001
From: Leann Ogasawara <leann.ogasawara at canonical.com>
Date: Mon, 21 Jun 2010 11:15:51 -0700
Subject: [PATCH] UBUNTU: [Config] Enable CONFIG_TASK_DELAY_ACCT=y

BugLink: http://bugs.launchpad.net/bugs/493156

Full reasoning is captured in the following thread:

https://lists.ubuntu.com/archives/kernel-team/2010-June/011238.html

"The request to enable CONFIG_TASK_DELAY_ACCT has once again come up per
a request from the IS team (I'ved CC'd elmo).  They could really use the
ability to use iotop to diagnose performance problems on our servers,
and they noted that other distributions have this option enabled."

Signed-off-by: Leann Ogasawara <leann.ogasawara at canonical.com>
---
 debian.master/config/config.common.ports  |    2 +-
 debian.master/config/config.common.ubuntu |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/debian.master/config/config.common.ports b/debian.master/config/config.common.ports
index be5e07d..b6e412f 100644
--- a/debian.master/config/config.common.ports
+++ b/debian.master/config/config.common.ports
@@ -3564,7 +3564,7 @@ CONFIG_TABLET_USB_GTCO=m
 CONFIG_TABLET_USB_KBTAB=m
 CONFIG_TADPOLE_TS102_UCTRL=m
 CONFIG_TASKSTATS=y
-# CONFIG_TASK_DELAY_ACCT is not set
+CONFIG_TASK_DELAY_ACCT=y
 CONFIG_TASK_IO_ACCOUNTING=y
 CONFIG_TASK_SIZE=0xc0000000
 CONFIG_TASK_XACCT=y
diff --git a/debian.master/config/config.common.ubuntu b/debian.master/config/config.common.ubuntu
index c6c7073..902ea7d 100644
--- a/debian.master/config/config.common.ubuntu
+++ b/debian.master/config/config.common.ubuntu
@@ -4232,7 +4232,7 @@ CONFIG_TABLET_USB_GTCO=m
 CONFIG_TABLET_USB_KBTAB=m
 CONFIG_TABLET_USB_WACOM=m
 CONFIG_TASKSTATS=y
-# CONFIG_TASK_DELAY_ACCT is not set
+CONFIG_TASK_DELAY_ACCT=y
 CONFIG_TASK_IO_ACCOUNTING=y
 CONFIG_TASK_XACCT=y
 CONFIG_TC1100_WMI=m
-- 
1.7.0.4



On Mon, 2010-06-21 at 10:22 -0700, Leann Ogasawara wrote:
> Hi All,
> 
> The request to enable CONFIG_TASK_DELAY_ACCT has once again come up per
> a request from the IS team (I'ved CC'd elmo).  They could really use the
> ability to use iotop to diagnose performance problems on our servers,
> and they noted that other distributions have this option enabled.  The
> option is described as follows:
> 
> config TASK_DELAY_ACCT
>         bool "Enable per-task delay accounting (EXPERIMENTAL)"
>         depends on TASKSTATS
>         help
>           Collect information on time spent by a task waiting for system
>           resources like cpu, synchronous block I/O completion and swapping
>           in pages. Such statistics can help in setting a task's priorities
>           relative to other tasks for cpu, io, rss limits etc.
> 
>           Say N if unsure.
> 
> Bug 493156 [1] captured the original request which we had marked as
> Won't Fix based on the following:
> 
> https://lists.ubuntu.com/archives/kernel-team/2009-December/008029.html
> 
> Tim wrote, "I think I just stirred the mud on this one. I've been
> chatting with Andy after he pointed out that this causes a performance
> hit. Its been around since 2.6.18 and we've not enabled it for any other
> release. Its used for intra-task prioritization. I only noticed it
> because iotop was complaining, which in retrospect, is an insufficient
> reason.  IMHO it should remain disabled."
> 
> However, there have been quite a bit of rebuttals to this decision.  In
> particular the upstream developer Balbir Singh notes in comment 9 of bug
> 493156 [2], "Can someone help characterize the performance hit with
> 'perf' data or oprofile data using a standard benchmark? When we
> developed the feature we ran a large set of benchmarks to ensure there
> is no visible performance hit. If there is a hit or a side-effect, I
> would be interested in fixing it upstream so that we can enable this
> feature in Ubuntu."
> 
> Additionally, Christian Kujau, notes the following in comment 4 of bug
> 493156 [3],
> "- Iotop doesn't work properly w/o CONFIG_TASK_DELAY_ACCT
> - There is no measurable overhead when enabled. I tried to measure in
> #532490, comment #6, but no winner there.
> @Tim/Andy: please elaborate on the 'performance hit' with this option
> enabled, I'm really curious if this is still valid for current kernels
> and which usecase has been tested to determine this hit.
> - The 'nodelayacct' can be used to disable delay accounting for those
> usecases where an actual performance hit can be seen.
> - All other major Linux distributions are doing it, only Ubuntu stands
> out :-\"
> 
> I'd be inclined to turn this on especially given the fact that you can
> disable it via the 'nodelayacct' kernel param.  However, I would like to
> know where we saw the original performance hit and how it was
> measured/tested to see if I could reproduce before enabling it.
> Thoughts? 
> 
> Thanks,
> Leann
> 
> [1] https://bugs.edge.launchpad.net/ubuntu/+bug/493156
> [2] https://bugs.edge.launchpad.net/ubuntu/+bug/493156/comments/9
> [3] https://bugs.edge.launchpad.net/ubuntu/+bug/493156/comments/4
> 
>