CHROMIUM: config: enable cgroup-based group scheduling

CHROMIUM: config: enable cgroup-based group scheduling

Group scheduling can have a dramatic impact on interactive response:

http://www.phoronix.com/scan.php?page=article&item=linux_2637_video

I think a reasonable group scheduling policy for ChromiumOS would be
to put the active tab processes into a "foreground" group and the
backgrounds tabs into a "background" group.

To simulate this, I did the following:

sudo mkdir -p /tmp/cgroup/cpu
sudo mount -t cgroup cgroup /tmp/cgroup/cpu -o cpu
sudo mkdir -m 0777 /tmp/cgroup/cpu/user
cd /tmp/cgroup/cpu/user
mkdir foreground
mkdir background
for i in `ps -ef | grep chrome | grep -v grep | awk '{ print $2 }'`; do
  echo $i > foreground/tasks
done

To simulate background tab processing I used 20 soaker threads:

$ cat busy.c


int main(int argc, char * argv[]) {
  int x = 0;

  while (1) {
    x++;
    if (x % 1000000 == 0) {
      sched_yield();
    }
  }
  return 0;
}

Which I than ran in the background:

echo $$ > background/tasks
for i in `seq 20`; do
  busy &
done

For the non-cgroup test case, I just did:

for i in `seq 20`; do
  busy &
done

Then in the browser I ran the SunSpider 0.9.1 JavaScript benchmark.

Without cgroups (i.e. without this patch) I get:

16954.8ms +/- 1.4%

With cgroups (i.e. this patch) and a background/foreground grouping I get:

2040.3ms +/- 2.0%

So I get an 8.3 X speedup using cgroups!

BUG=9288
TEST=See above.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>;
Change-Id: I16c87499dfe35ff5b2f5353e68db447b9ce10ddc

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=a87ecbb

[Mandeep Singh Baines, 2011-01-10 23:23:11]

PTAL. Updated to latest kernel. Since this CL was originally sent out, we
disabled CGROUPS. Did a quick sanity check to make sure there is no performance
impact to enabling CGROUPS.

Boot performance
================

Before:

  rdbytes_kernel_to_chrome_exec                                   58725376.0
  rdbytes_kernel_to_chrome_main                                   93996032.0
  rdbytes_kernel_to_login                                         99543040.0
  rdbytes_kernel_to_startup                                       9854976.0
  rdbytes_kernel_to_startup_done                                  12690432.0
  rdbytes_kernel_to_x_started                                     58291200.0
  reboots_in_syslog                                               11
  seconds_firmware_boot                                           2.12
  seconds_kernel_to_chrome_exec                                   4.43
  seconds_kernel_to_chrome_main                                   5.75
  seconds_kernel_to_login                                         6.97
  seconds_kernel_to_network                                       11.75
  seconds_kernel_to_startup                                       1.85
  seconds_kernel_to_startup_done                                  2.21
  seconds_kernel_to_x_started                                     4.32
  seconds_power_on_to_login                                       9.09
  seconds_reboot_time                                             5.96262
  seconds_shutdown_time                                           3.84262

After:

  rdbytes_kernel_to_chrome_exec                                   56587264.0
  rdbytes_kernel_to_chrome_main                                   95097856.0
  rdbytes_kernel_to_login                                         99620864.0
  rdbytes_kernel_to_startup                                       9854976.0
  rdbytes_kernel_to_startup_done                                  12690432.0
  rdbytes_kernel_to_x_started                                     53748736.0
  reboots_in_syslog                                               11
  seconds_firmware_boot                                           2.15
  seconds_kernel_to_chrome_exec                                   4.35
  seconds_kernel_to_chrome_main                                   5.71
  seconds_kernel_to_login                                         6.92
  seconds_kernel_to_network                                       11.88
  seconds_kernel_to_startup                                       1.85
  seconds_kernel_to_startup_done                                  2.2
  seconds_kernel_to_x_started                                     4.21
  seconds_power_on_to_login                                       9.07
  seconds_reboot_time                                             6.217651
  seconds_shutdown_time                                           4.067651

Sun Spider 0.9.1
================

Before:

1675.4ms +/- 1.7%

After:

1658.6ms +/- 4.0%

[Greg Spencer (Chromium), 2011-01-11 23:42:29]

LGTM, but I'm no kernel expert.

[Mandeep Singh Baines, 2011-01-13 00:02:58]

ping

Will, Olof, would like to have one of you two review also.

[Olof Johansson, 2011-01-13 05:17:29]

Seems like we're turning CGROUPS on and off on a weekly basis these days. :-)

I'm OK with enabling it myself. Looks like there's some potential benefits in
doing it. So LGTM.