> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> Harry Smith
> Sent: 10 May 2007 09:24
> To: Atsushi SAKAI
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] fair scheduling
>
> Hi,
>
> that's true. But dom0 has 4 VCPUs mapped on 2 physical CPU.
> CPU usage -->
> case1) when vm2 doesn't have any load
> dom0 20-25% vm1 100% vm2 0%
>
> case2) when vm2 has a compute-intense load
> dom0 20-25% vm1 100% vm2 100%
>
> So my question is that in this case there is 200% of CPU
> available to dom0, still it is using only 20-25%, but in
> case2 webserver throughput in vm1 goes down by 15-20%. Why
> this is so?
Here are some architectural features that may affect things:
1. Are PCPU's "real" CPU cores or HyperThreaded "virtual" cores? If the
latter, the answer to why performance goes down is obvious... [Sorry if
you covered this in an earlier mail]
2. Is it possible that cache-contention is affecting the performance?
3. Is it possible that memory bandwidth is affecting the performance?
4. Is it possible that Page-table/TLB contention is affecting
performance?
> Why dom0 can't use more CPU to process vm1 & vm2 requests
> separately ? As we are trying to show that vm1, vm2 are two
> OS running independetly, why they affect each other's performance ?
Because there are still running on shared hardware, so one OS's
behaviour will affect the overall hardware load, perhaps? I'm not saying
it is so, but I suspect it's at least part of the answer.
--
Mats
>
> thanks,
> Harry
>
>
>
>
> On 5/10/07, Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> You should check I/O behavior.
>
> If I/O occured,
> other domain(vm1, vm2) data is handled by dom0 as driver domain.
>
> Thanks
> Atsushi SAKAI
>
>
> "Harry Smith" < harry.smith272@xxxxxxxxx
> <mailto:harry.smith272@xxxxxxxxx> > wrote:
>
> > Hi Atsushi & Pradeep,
> >
> > thanks for replying back.
> > I have 4 VCPUs for each of VM. But the point I
> wanted to stress upon is -
> > "This happened even in the case where CPU usage by
> both of vm1,vm2 is
> > restricted to 100% each. "
> > I had pinned all 4 VCPUs of each VM to a single phys.
> CPU. & I have 4 phys.
> > CPUs
> > means my vm1 was using cpu1, vm2 using cpu2 &
> domain-0 using cpu0,cpu3
> >
> > Problem is when there is no load on vm2, webserver
> performance of vm1 is
> > better. But when vm2 has some compute-intense load
> then vm1 webserver
> > performance goes down.
> > Please note that CPU consumption of vm1 shown by
> xentop in both cases is
> > 100%, still webserver performance goes down by around 15-20%.
> > Even after trying to isolate two VMs, existence of
> load on one VM is
> > affecting other.
> >
> > so is it expected behavior ?
> >
> > thanks,
> > Harry
> >
> >
> >
> > On 5/10/07, pradeep singh rautela <rautelap@xxxxxxxxx> wrote:
> > >
> > >
> > >
> > > On 5/10/07, Atsushi SAKAI < sakaia@xxxxxxxxxxxxxx> wrote:
> > > >
> > > > One vcpu can use one pcpu at one time.
> > > > It means 100% is maxium for one vcpu domain.
> > > > If you want to use cpu resources, you should set
> more vcpu.
> > >
> > >
> > > Ok, this explains a lot of things.
> > > As i understand this , more VCPUs means more
> freedom to hypervisor to
> > > migrate them among physical CPUs, depending on the
> free PCPUs available.
> > >
> > > In general
> > >
> > > domU1
> > > / | \
> > > vcpu1 vcpu2 vcpu3
> > >
> > > pcpu1 pcpu2 pcpu3 pcpu4 pcpu5 pcpu6
> > >
> > > I mean ,domU1 can run on any vcpu , right? now
> vcpu1, vcpu2, vcpu3 share a
> > > one to many reationship between pcpus[1....6]. That
> is a vcpu can run on any
> > > of the pcus available to the Xen hypervisor(unless
> i explicitly pin it to ).
> > >
> > >
> > > Is my naive understanding of what you explained is correct?
> > >
> > > Thank you
> > > ~psr
> > >
> > > > Thanks
> > > > Atsushi SAKAI
> > > >
> > > >
> > > > "pradeep singh rautela" <rautelap@xxxxxxxxx> wrote:
> > > >
> > > > > Hi Atsushi,
> > > > >
> > > > > On 5/10/07, Atsushi SAKAI <
> sakaia@xxxxxxxxxxxxxx> wrote:
> > > > > >
> > > > > >
> > > > > > You should show detail configuration.
> > > > > > Your information is too short.
> > > > > >
> > > > > > Anyway I guess each domain has one vcpu.
> > > > > > If so, this is normal behavior.
> > > > > > Because one vcpu cannot allocate two or more
> pcpu at once.
> > > > >
> > > > >
> > > > > Right, but shouldn't Xen hypervisor be capable
> of migrating the VCPU
> > > > among
> > > > > the available PCPUs on a multiprocessor system,
> like in this case? And
> > > > > criteria should be the load on the PCPU or the
> idle PCPUs.
> > > > > yes/no?
> > > > >
> > > > > Am i missing something here?
> > > > >
> > > > > Thanks
> > > > > ~psr
> > > > >
> > > > > Thanks
> > > > > > Atsushi SAKAI
> > > > > >
> > > > > > "Harry Smith" < harry.smith272@xxxxxxxxx
> <mailto:harry.smith272@xxxxxxxxx> > wrote:
> > > > > >
> > > > > > > hi all,
> > > > > > >
> > > > > > > I am using xen3.0.3 on dual core
> hyperthreaded processor (in all 4
> > > > > > cores).
> > > > > > > There are 2 VMs vm1,vm2 among which vm1 has
> a webserver running on
> > > > it.
> > > > > > >
> > > > > > > While testing the performance of webserver,
> when I introduce some
> > > > load
> > > > > > on
> > > > > > > vm2 which involves some computations the
> webserver performance
> > > > goes
> > > > > > down.
> > > > > > > This happened even in the case where CPU
> usage by both of vm1,vm2
> > > > is
> > > > > > > restricted to 100% each.
> > > > > > >
> > > > > > > Is it expected behavior ? if yes then how
> does one can control
> > > > addition
> > > > > > of
> > > > > > > new virtual machines as adding every new VM
> will result in
> > > > lowering
> > > > > > > performance of other VMs. Through
> scheduling parameters we can
> > > > just
> > > > > > specify
> > > > > > > amount of CPU to be used in relative sense
> (weight) & upper limit
> > > > (cap).
> > > > > > But
> > > > > > > how to tackle this point.
> > > > > > >
> > > > > > > I am new in this area & wanna set up a lab
> using virtualization,
> > > > so want
> > > > > > to
> > > > > > > find solution for this.
> > > > > > >
> > > > > > > thanks,
> > > > > > > Harry
> > > > > > >
> > > > > > > we always have a choice...
> > > > > >
> > > > > >
> > > > > >
> > > > > > _______________________________________________
> > > > > > Xen-devel mailing list
> > > > > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > > > > http://lists.xensource.com/xen-devel
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > ---
> > > > > pradeep singh rautela
> > > > >
> > > > > "Genius is 1% inspiration, and 99%
> perspiration" - not me :)
> > > >
> > > >
> > > >
> > >
> > >
> > > --
> > > ---
> > > pradeep singh rautela
> > >
> > > "Genius is 1% inspiration, and 99% perspiration" -
> not me :)
> > >
>
>
>
>
>
>
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