答复: [Xen-devel] Credit scheduler vs SEDF scheduler

["Zhiyuan Shao" <zyshao.maillist@gmail.com>]

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Hi,

 

Your experiment results are actually “expected”. There are several reasons
make the results happen. 

 

Firstly, Credit has long time slice (i.e., 30 millisec by default), and this
make the observed close-to 30ms RTT to happen, actually, during such long
RTT (the spike), the domain in test (domain 1 of your experiment) is just
scheduled-out (actually, I guess the spikes illustrated in your figure 1
should read higher than 30ms!). At the same time, the scheduled-in vcpus
(may executing the TEST program, which is cpu-hogs), and they will not give
up their 30-ms time slice if they are not preempted. 

 

Secondly, as regulated by Credit scheduler, if a VCPU has no more credits,
it will not be BOOSTed even it do have some I/O requests to handle. This
explains why your figure1, which has little spikes in the first 150 second,
and crowed spikes follow. Since vcpu of domain 1 simply used out their
credits, and can not preempt the other running vcpus of other domains, even
they do have I/O operations to accomplish (i.e., PING). 

 

Lastly, compared with Credit, SEDF generally has short time slices, and it
has bigger chances to preempt current running vcpu when another vcpu found
it has some I/O operations to be accomplished. (actually, I donot understand
SEDF very well, but conclude these features by reading the trace data)

 

Actually, you can use BCredit patch to eliminate the spikes, I can guarantee
that it will work very well! :-) And I agree with George that you should not
use PING to justify whether a scheduler is good or not.

 

Best,

Zhiyuan

 

 

  _____  

发件人: xen-devel-bounces@lists.xensource.com
[mailto:xen-devel-bounces@lists.xensource.com] 代表 gaurav somani
发送时间: 2009年5月5日 17:26
收件人: xen-devel@lists.xensource.com
主题: [Xen-devel] Credit scheduler vs SEDF scheduler

 

Hi list,

I am evaluating the scheduler behavior in xen.

I am using Xen 3.3.0 
Dom0 and Dom1,2,3 and 4 all are opensuse 11.
I have one CPU Intensive TEST which has no. of arithmatic instruction in an
infinite while() loop.
i am pinging domain1 with an external machine. and noting the RTT values.

i have below experiments
time (s)          domain state
0                 dom0,1,2,3,4 all idle
50               dom2 TEST started
100             dom3 TEST started
150             dom4 TEST started
200             dom0 TEST started
250             dom2 TEST stopped
300             dom3 TEST stopped
350             dom4 TEST stopped
400             dom0 TEST stopped

For these 400 seconds time, i have performed experiments with Credit and
SEDF sceduler.
the configuration is 


Credit configuration - weight 256, cap 0
Domain                  VCPU 
0                                  2
1                                  2
2                                  2
3                                  2
4                                  2
all vcpu0s are pinned to pcpu0 and vcpu1s to pcpu1.


SEDF configuration - Period 10ms slice - 1.9ms
Domain                  VCPU 
0                                  2
1                                  2
2                                  2
3                                  2
4                                  2
all vcpu0s are pinned to pcpu0 and vcpu1s to pcpu1.

the results of RTT values are attached herewith. the performance of Credit
is very bad in comparison to SEDF in this scenario.
Please provide me some thought on it.


Thanks and Regards

Gaurav somani
M.Tech (ICT)
Dhribhai Ambani Institute of ICT,
INDIA

http://dcomp.daiict.ac.in/~gaurav <http://dcomp.daiict.ac.in/%7Egaurav> 






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