LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
* question: cpu.shares and parent-children relationshp in the hierarchy
@ 2011-02-16  0:11 Michal Soltys
  2011-02-17  2:00 ` Yong Zhang
  0 siblings, 1 reply; 2+ messages in thread
From: Michal Soltys @ 2011-02-16  0:11 UTC (permalink / raw)
  To: lkml

Hi,

I've been testing how this works in practice, and I have few 
configurations I'm not sure why they behave the way they do.

All the test processes just drain cpu with an infinite loop. 
All of them are pinned to single cpu core. cgroup with just 
-o cpu is mounted, and the scenario is following (in brackets 
- assigned cpu.shares):

    root(1024)
   /          \
Y(1024)      X(4096)
            /       \
         A(8192)   B(8192)

Four test processes sit in X, Y, A and B; root is "empty"
(effectively idle processes). The one in Y expectedly gets 
20% cpu, A and B divide the cpu share equally, but - why do 
the process in X gets only ~4.75% ? Essentially:

11:36:45 PM       PID    %usr %system  %guest    %CPU   CPU  Command
11:36:50 PM     29472   20.00    0.00    0.00   20.00     1  loadme(y)
11:36:50 PM     29473    4.80    0.00    0.00    4.80     1  loadme(x)
11:36:50 PM     29474   37.60    0.00    0.00   37.60     1  loadme(a)
11:36:50 PM     29475   37.60    0.00    0.00   37.60     1  loadme(b)

In the other words - what is the intended relation between ancestor's 
cpu.shares and its children ? Looking at the example above, it looks 
like the task in X should get 4/5 (root unused, 1/5 for Y, the rest 
for X subtree) * 1/5 (from assigned values in X subtree, 
4096/20480) - but that would be ~16%.

The task in X behaves like if X had 1024 - maybe it's always assumed 
when parent-children relationship is considered, and the actual value 
is used only when dividing cpu between siblings ?

If I move the test task from X to root, the situation will change to:

11:56:49 PM       PID    %usr %system  %guest    %CPU   CPU  Command
11:56:54 PM     29472   16.60    0.00    0.00   16.60     1  loadme(y)
11:56:54 PM     29473   16.60    0.00    0.00   16.60     1  loadme(root)
11:56:54 PM     29474   33.20    0.20    0.00   33.40     1  loadme(a)
11:56:54 PM     29475   33.40    0.00    0.00   33.40     1  loadme(b)

In this scenario, everything seems as expected - 1/6 for Y, 1/6 for root, 
4/6 for X subtree.


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: question: cpu.shares and parent-children relationshp in the hierarchy
  2011-02-16  0:11 question: cpu.shares and parent-children relationshp in the hierarchy Michal Soltys
@ 2011-02-17  2:00 ` Yong Zhang
  0 siblings, 0 replies; 2+ messages in thread
From: Yong Zhang @ 2011-02-17  2:00 UTC (permalink / raw)
  To: Michal Soltys; +Cc: lkml

On Wed, Feb 16, 2011 at 8:11 AM, Michal Soltys <soltys@ziu.info> wrote:
> Hi,
>
> I've been testing how this works in practice, and I have few
> configurations I'm not sure why they behave the way they do.
>
> All the test processes just drain cpu with an infinite loop.
> All of them are pinned to single cpu core. cgroup with just
> -o cpu is mounted, and the scenario is following (in brackets
> - assigned cpu.shares):
>
>    root(1024)
>   /          \
> Y(1024)      X(4096)
>            /       \        \
>         A(8192)   B(8192)  task-x(1024)

I assume loadme(x) is an process of group X, like above.

If so, there isn't any problem with it.

Thanks,
Yong

>
> Four test processes sit in X, Y, A and B; root is "empty"
> (effectively idle processes). The one in Y expectedly gets
> 20% cpu, A and B divide the cpu share equally, but - why do
> the process in X gets only ~4.75% ? Essentially:
>
> 11:36:45 PM       PID    %usr %system  %guest    %CPU   CPU  Command
> 11:36:50 PM     29472   20.00    0.00    0.00   20.00     1  loadme(y)
> 11:36:50 PM     29473    4.80    0.00    0.00    4.80     1  loadme(x)
> 11:36:50 PM     29474   37.60    0.00    0.00   37.60     1  loadme(a)
> 11:36:50 PM     29475   37.60    0.00    0.00   37.60     1  loadme(b)
>
> In the other words - what is the intended relation between ancestor's
> cpu.shares and its children ? Looking at the example above, it looks
> like the task in X should get 4/5 (root unused, 1/5 for Y, the rest
> for X subtree) * 1/5 (from assigned values in X subtree,
> 4096/20480) - but that would be ~16%.
>
> The task in X behaves like if X had 1024 - maybe it's always assumed
> when parent-children relationship is considered, and the actual value
> is used only when dividing cpu between siblings ?
>
> If I move the test task from X to root, the situation will change to:
>
> 11:56:49 PM       PID    %usr %system  %guest    %CPU   CPU  Command
> 11:56:54 PM     29472   16.60    0.00    0.00   16.60     1  loadme(y)
> 11:56:54 PM     29473   16.60    0.00    0.00   16.60     1  loadme(root)
> 11:56:54 PM     29474   33.20    0.20    0.00   33.40     1  loadme(a)
> 11:56:54 PM     29475   33.40    0.00    0.00   33.40     1  loadme(b)
>
> In this scenario, everything seems as expected - 1/6 for Y, 1/6 for root,
> 4/6 for X subtree.
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>



-- 
Only stand for myself

^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2011-02-17  2:00 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-02-16  0:11 question: cpu.shares and parent-children relationshp in the hierarchy Michal Soltys
2011-02-17  2:00 ` Yong Zhang

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).