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Message-ID: <20110608163234.GA23031@linux.vnet.ibm.com>
Date: Wed, 8 Jun 2011 22:02:34 +0530
From: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
To: Vladimir Davydov <vdavydov@...allels.com>
Cc: Paul Turner <pjt@...gle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Bharata B Rao <bharata@...ux.vnet.ibm.com>,
Dhaval Giani <dhaval.giani@...il.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Pavel Emelianov <xemul@...allels.com>
Subject: Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs
unpinned
* Vladimir Davydov <vdavydov@...allels.com> [2011-06-08 14:46:06]:
> On Tue, 2011-06-07 at 19:45 +0400, Kamalesh Babulal wrote:
> > Hi All,
> >
> > In our test environment, while testing the CFS Bandwidth V6 patch set
> > on top of 55922c9d1b84. We observed that the CPU's idle time is seen
> > between 30% to 40% while running CPU bound test, with the cgroups tasks
> > not pinned to the CPU's. Whereas in the inverse case, where the cgroups
> > tasks are pinned to the CPU's, the idle time seen is nearly zero.
>
> (snip)
>
> > load_tasks()
> > {
> > for (( i=1; i<=5; i++ ))
> > do
> > jj=$(eval echo "\$NR_TASKS$i")
> > shares="1024"
> > if [ $PRO_SHARES -eq 1 ]
> > then
> > eval shares=$(echo "$jj * 1024" | bc)
> > fi
> > echo $hares > $MOUNT/$i/cpu.shares
> ^^^^^
> a fatal misprint? must be shares, I guess
>
> (Setting cpu.shares to "", i.e. to the minimal possible value, will
> definitely confuse the load balancer)
My bad. It was fatal typo, thanks for pointing it out. It made a big difference
in the idle time reported. After correcting to $shares, now the CPU idle time
reported is 20% to 22%. Which is 10% less from the previous reported number.
(snip)
There have been questions on how to interpret the results. Consider the
following test run without pinning of the cgroups tasks
Average CPU Idle percentage 20%
Bandwidth shared with remaining non-Idle 80%
Bandwidth of Group 1 = 7.9700% i.e = 6.3700% of non-Idle CPU time 80%
|...... subgroup 1/1 = 50.0200 i.e = 3.1800% of 6.3700% Groups non-Idle CPU time
|...... subgroup 1/2 = 49.9700 i.e = 3.1800% of 6.3700% Groups non-Idle CPU time
For example let consider the cgroup1 and sum_exec time is the 7 field
captured from the /proc/sched_debug
while1 27273 30665.912793 1988 120 30665.912793 30909.566767 0.021951 /1/2
while1 27272 30511.105690 1995 120 30511.105690 30942.998099 0.017369 /1/1
-----------------
61852.564866
-----------------
- The bandwidth for sub-cgroup1 of cgroup1 is calculated = (30909.566767 * 100) / 61852.564866
= ~50%
and sub-cgroup2 of cgroup1 is calculated = (30942.998099 * 100) / 61852.564866
= ~50%
In the similar way If we add up the sum_exec of all the groups its
------------------------------------------------------------------------------------------------
Group1 Group2 Group3 Group4 Group5 sum_exec
------------------------------------------------------------------------------------------------
61852.564866 + 61686.604930 + 122840.294858 + 232576.303937 +296166.889155 = 775122.657746
again taking the example of cgroup1
Total percentage of bandwidth allocated to cgroup1 = (61852.564866 * 100) / 775122.657746
= ~ 7.9% of total bandwidth of all the cgroups
Calculating the non-idle time is done with
Total (execution time * 100) / (no of cpus * 60000 ms) [script is run for a 60 seconds]
i.e. = (775122.657746 * 100) / (16 * 60000)
= ~80% of non-idle time
Percentage of bandwidth allocated to cgroup1 of the non-idle is derived as
= (cgroup bandwith percentage * non-idle time) / 100
= for cgroup1 = (7.9700 * 80) / 100
= 6.376% bandwidth allocated of non-Idle CPU time.
Bandwidth of Group 2 = 7.9500% i.e = 6.3600% of non-Idle CPU time 80%
|...... subgroup 2/1 = 49.9900 i.e = 3.1700% of 6.3600% Groups non-Idle CPU time
|...... subgroup 2/2 = 50.0000 i.e = 3.1800% of 6.3600% Groups non-Idle CPU time
Bandwidth of Group 3 = 15.8400% i.e = 12.6700% of non-Idle CPU time 80%
|...... subgroup 3/1 = 24.9900 i.e = 3.1600% of 12.6700% Groups non-Idle CPU time
|...... subgroup 3/2 = 24.9900 i.e = 3.1600% of 12.6700% Groups non-Idle CPU time
|...... subgroup 3/3 = 25.0600 i.e = 3.1700% of 12.6700% Groups non-Idle CPU time
|...... subgroup 3/4 = 24.9400 i.e = 3.1500% of 12.6700% Groups non-Idle CPU time
Bandwidth of Group 4 = 30.0000% i.e = 24.0000% of non-Idle CPU time 80%
|...... subgroup 4/1 = 13.1600 i.e = 3.1500% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/2 = 11.3800 i.e = 2.7300% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/3 = 13.1100 i.e = 3.1400% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/4 = 12.3100 i.e = 2.9500% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/5 = 12.8200 i.e = 3.0700% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/6 = 11.0600 i.e = 2.6500% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/7 = 13.0600 i.e = 3.1300% of 24.0000% Groups non-Idle CPU time
|...... subgroup 4/8 = 13.0600 i.e = 3.1300% of 24.0000% Groups non-Idle CPU time
Bandwidth of Group 5 = 38.2000% i.e = 30.5600% of non-Idle CPU time 80%
|...... subgroup 5/1 = 48.1000 i.e = 14.6900% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/2 = 6.7900 i.e = 2.0700% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/3 = 6.3700 i.e = 1.9400% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/4 = 5.1800 i.e = 1.5800% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/5 = 5.0400 i.e = 1.5400% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/6 = 10.1400 i.e = 3.0900% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/7 = 5.0700 i.e = 1.5400% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/8 = 6.3900 i.e = 1.9500% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/9 = 6.8800 i.e = 2.1000% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/10 = 6.4700 i.e = 1.9700% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/11 = 6.5600 i.e = 2.0000% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/12 = 4.6400 i.e = 1.4100% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/13 = 7.4900 i.e = 2.2800% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/14 = 5.8200 i.e = 1.7700% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/15 = 6.5500 i.e = 2.0000% of 30.5600% Groups non-Idle CPU time
|...... subgroup 5/16 = 5.2700 i.e = 1.6100% of 30.5600% Groups non-Idle CPU time
Thanks,
Kamalesh.
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