[rhelv6-beta-list] A simple program runs under KVM faster than under nake PC.

[Kirby Zhou]

A simple fact is that RHEL5 DO NOT have KSM.

RHEL6/nake
[root at djt_10_47 ~]# echo 2 > /sys/kernel/mm/ksm/run
[root at xen-727057^10.227 ~]# time ssh 10.12.10.47 ./a.out 1 10000   
crc:a4580383

real    0m5.628s
user    0m0.000s
sys     0m0.000s

RHEL6/KVM
[root at djt_10_199 ~]# echo 2 > /sys/kernel/mm/ksm/run
[root at xen-727057^10.227 ~]# time ssh 10.12.10.199 ./a.out 1 10000  
crc:a4580383

real    0m3.139s
user    0m0.000s
sys     0m0.000s

  Regards
  Kirby Zhou

-----Original Message-----
From: rhelv6-beta-list-bounces at redhat.com
[mailto:rhelv6-beta-list-bounces at redhat.com] On Behalf Of Sean Pajot
Sent: Monday, August 09, 2010 1:34 AM
To: Red Hat Enterprise Linux 6 (Santiago) Beta releases discussion
mailing-list
Subject: Re: [rhelv6-beta-list] A simple program runs under KVM faster than
under nake PC.

Crazy idea. How "simple" is this program? If you're using KVM, then KSM will

be merging identical pages. This can benefit CPU cache lines. Would this 
account for the performance improvement?

Try turning off KSM, power down/up your test VM to flush all the pages, and 
test again. It should also be possible to modify your app to use KSM for 
itself on bare metal.

Kirby Zhou wrote:
> 
> 
> Both RHEL5/RHEL6 encounter the same situation.
> 
> Is there any potential bug?
> 
>  
> 
> ]# g++ testaes.cpp -lcrypto -lz
> 
>  
> 
> RHEL6 nake
> 
> [root at djt_10_47 ~]# time ./a.out 1 10000 | head -n 10000 | md5sum
> 
> caba4fd0bae809e634b5cd8acd3424f2  -
> 
>  
> 
> real    0m5.778s
> 
> user    0m5.774s
> 
> sys     0m0.014s
> 
>  
> 
> RHEL6 KVM
> 
> [root at djt_10_199 ~]# time ./a.out 1 10000 | head -n 10000 | md5sum
> 
> 51722dcdf339f131a89eb2dc106d8dbe  -
> 
>  
> 
> real    0m3.272s
> 
> user    0m3.266s
> 
> sys     0m0.032s
> 
>  
> 
> RHEL5 nake
> 
> [@djt_10_48 ~]# time ./a.out 1 10000 | head -n 10000 | md5sum
> 
> 51722dcdf339f131a89eb2dc106d8dbe  -
> 
>  
> 
> real    0m5.786s
> 
> user    0m5.780s
> 
> sys     0m0.008s
> 
>  
> 
> RHEL5 KVM
> 
> [@djt_10_192 ~]# time ./a.out 1 10000 | head -n 10000 | md5sum         
> 
> 51722dcdf339f131a89eb2dc106d8dbe  -
> 
>  
> 
> real    0m3.243s
> 
> user    0m2.864s
> 
> sys     0m0.387s
> 
>  
> 
>  
> 
>  
> 
>   Regards
> 
>   Kirby Zhou
> 
>  

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