Re: Lost of performance over AMD-V with KVM?

[Gleb Natapov <gleb@redhat.com>]

On Thu, Jul 11, 2013 at 02:52:40PM +0200, Victor fernandez wrote:
> Hi Gleb,
> 
>     you were right, we update the qemu-kvm to 1.0 and now
>     the S.L. instance start with new cpu flags (for instance:
> 3dnowext,3dnow).
> 
>     But we have bad performance still, around 17% of lost in
>     our AMD processors. Let me explain better, we are running
>     three different hight energy physic softwares. And in 2 of them
>     we don't have any problem with the performances, 4-5% of lost.
>     But in the other one (GAUSS, LHCb software), and only in
>     AMD-V virtualization we have arount 17%-33% lost performance
>     depending on the processor number. But Gauss software in
>     Intel processor are running with an acceptable performance.
> 
>     And we suspected that could be due to cpu flags, but now we are not
>     sure about that because now 3dnowext,3dnow are included
>     and the performances are still bad. But these flags are not yet
> included
>     with qemu-kvm_1.0.
> 
> > ht > rdtscp > constant_tsc > nopl > nonstop_tsc > amd_dcm >
> monitor > extapic > ibs > skinit > wdt > nodeid_msr > hw_pstate >
> lbrv > svm_lock > pausefilter
> 
>     - Do you think that these flags could be the problem?
Non of them are related to an instruction set relevant for performance.
amd_dcm is a synthetic flag (meaning that it does not correspond to any
real cpuid) that says that your machine is NUMA. Can you bind you VM to
single numa node with taskset/numactl?

I see that you assign only 2G to your VM, may be this is not enough?
How much memory host has?

>     - Do you have any idea what could it be?
> 
>     Thanks in advance Gleb,
>         Víctor Fdez.
> 
> 
> El 09/07/13 18:08, Gleb Natapov escribió:
> >On Tue, Jul 09, 2013 at 05:30:26PM +0200, Victor fernandez wrote:
> >>Hi Gleb,
> >>
> >>     root@vfalbor-desktop:~# uname -a
> >>*Linux vfalbor-desktop 2.6.32-24-generic *#43-Ubuntu SMP Thu Sep 16
> >>14:58:24 UTC 2010 x86_64 GNU/Linux
> >>
> >>     root@vfalbor-desktop:~# dpkg --list | grep qemu
> >>     ii  qemu-common *0.12.3+noroms-0ubuntu9.21 * qemu common
> >>functionality (bios, documentati
> >>     ri  qemu-kvm *0.12.3+noroms-0ubuntu9.21*
> >>Full virtualization on i386 and amd64 hardwa
> >>
> >Ugh, those are ancient and vendor packages. I thought you were running
> >Scientific Linux 6 as a host too which also has vendor specific
> >packages, but at least something that I can easily look into :)
> >Can you reproduce with upstream kernel/qemu? If it works on upstream you
> >can open bug in Ubuntu.
> >
> >>     One of the things that we did, we try to update libvirt to the
> >>last versions
> >>     because we are using for our cloud the version of ubuntu 10.04 and the
> >>     last stable version of libvirt was 0.7.5-5ubuntu27.23, but when
> >>we try to
> >>     get the capabilities, we get the following:
> >This is definitely not libvirt fault. This is either kernel or qemu.
> >Looking into git history 3dnow/3dnowext support was introduce into the
> >kernel kvm component before 2.6.32 though.
> >
> >>     root@vfalbor-desktop:~/# virsh capabilities | grep 3dnow
> >>       <feature name='*3dnowprefetch*'/>
> >>     root@vfalbor-desktop:~/#
> >>
> >>     but in the cpu_map.xml file we find the 3dnow and 3dnowext for
> >>our architecture:
> >>
> >>     root@vfalbor-desktop:~/# cat /usr/share/libvirt/cpu_map.xml |
> >>grep 3dnow
> >>             <feature name='*3dnowext*'> <!-- CPUID_EXT2_3DNOWEXT -->
> >>             <feature name='3dnow'> <!-- CPUID_EXT2_3DNOW -->
> >>             <feature name='3dnowprefetch'> <!--
> >>CPUID_EXT3_3DNOWPREFETCH -->
> >>
> >>     Thanks Gleb,
> >>         Víctor Fdez.
> >>
> >>El 09/07/13 17:16, Gleb Natapov escribió:
> >>>On Tue, Jul 09, 2013 at 05:07:57PM +0200, Victor fernandez wrote:
> >>>>Yep,
> >>>>
> >>>>     -> this is for the host:
> >>>>
> >>>>     root@vfalbor-desktop:~# cat /proc/cpuinfo | grep flags | uniq
> >>>>     flags        : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr
> >>>>pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx
> >>>>mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc
> >>>>rep_good nonstop_tsc extd_apicid amd_dcm pni monitor cx16 popcnt
> >>>>lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse
> >>>>3dnowprefetch osvw ibs skinit wdt nodeid_msr
> >>>>
> >>>>     -> this is for the VM:
> >>>>     [root@sl6 ~]# cat /proc/cpuinfo | grep flags | uniq
> >>>>     flags        : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr
> >>>>pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext
> >>>>fxsr_opt pdpe1gb lm rep_good extd_apicid pni cx16 popcnt lahf_lm
> >>>>cmp_legacy cr8_legacy abm sse4a misalignsse 3dnowprefetch
> >>>>
> >>>Hmm, what is your kernel and qemu versions?
> >>>
> >>>>El 09/07/13 17:00, Gleb Natapov escribió:
> >>>>>On Tue, Jul 09, 2013 at 04:57:13PM +0200, Victor fernandez wrote:
> >>>>>>     2.- with the "-cpu host" parameter:
> >>>>>>
> >>>>>>/usr/bin/kvm *-cpu host* -m 2048 -smp 1 -name i-2-11-VM -monitor
> >>>>>>telnet:127.0.0.1:9941,server,nowait -boot c /mnt/b07f7f29-7b9b-3d4b-b170-77876d10e7b1/134bc689-1207-487c-ae95-6c0dc2e0f285
> >>>>>>-parallel none -usb -usbdevice tablet -vnc :0 -vga cirrus -net
> >>>>>>nic,macaddr=06:00:90:00:00:08,vlan=0,model=e1000,name=e1000.0 -net
> >>>>>>tap,script=/usr/bin/qemu-ifup,vlan=0,name=tap.0
> >>>>>>
> >>>>>With this command line can you provide output of /proc/cpuinfo on the
> >>>>>host and the guest?
> >>>>>
> >>>>>--
> >>>>>			Gleb.
> >>>>>--
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> >>>--
> >>>			Gleb.
> >--
> >			Gleb.

--
			Gleb.