incubator-cloudstack-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Alex Huang <Alex.Hu...@citrix.com>
Subject RE: Vmware CPU Cap
Date Wed, 23 May 2012 20:43:52 GMT
I'm surprised.  I definitely recall having that conversation before about never exceeding the
physical limits of the hypervisor.  I'm pretty sure we have test cases against that as well.

--Alex

> -----Original Message-----
> From: Edison Su [mailto:Edison.su@citrix.com]
> Sent: Wednesday, May 23, 2012 1:39 PM
> To: cloudstack-dev@incubator.apache.org
> Subject: RE: Vmware CPU Cap
> 
> I think it's a general issue for all the hypervisors we supported.
> 
> > -----Original Message-----
> > From: Alex Huang [mailto:Alex.Huang@citrix.com]
> > Sent: Wednesday, May 23, 2012 1:32 PM
> > To: cloudstack-dev@incubator.apache.org
> > Subject: RE: Vmware CPU Cap
> >
> > That's because no one wrote a host allocator for VmWare.
> >
> > The relationship between DeploymentPlanner and HostAllocator and
> > StoragePoolAllocator is as follows:
> >
> > DeploymentPlanner deals with heuristics and affinity rules of placing
> > a VM.  Once it determines a set of hosts that matches, it then asks
> > the HostAllocator to work on the limitations of the type of hypervisor.
> > There was never a HostAllocator written for VmWare.  It just uses the
> > one that was written originally for XenServer.  Hence the bug.
> >
> > There's similar differentiation for DeploymentPlanner and
> > StoragePoolAllocator and similar bugs exists, especially if someone
> > adds a completely new type of storage pool but decides to just reuse
> > the current set of StoragePoolAllocators.
> >
> > --Alex
> >
> > > -----Original Message-----
> > > From: Edison Su [mailto:Edison.su@citrix.com]
> > > Sent: Wednesday, May 23, 2012 1:24 PM
> > > To: cloudstack-dev@incubator.apache.org; 'tamasm@veber.co.uk'
> > > Subject: RE: Vmware CPU Cap
> > >
> > > Thanks for your input, I find another bug in cloudstack...
> > > Let's dive little bit deeper into how the CPU allocation works.
> > > VMware(the same for other hypervisors(Xen/KVM)) uses proportional
> > share
> > > based scheduling algorithm([1],[2]). It means "If a virtual machine
> > has twice
> > > as many shares of a resource as another virtual machine, it is
> > entitled to
> > > consume twice as much of that resource when these two virtual
> > machines
> > > are competing for resources."
> > > There are two questions:
> > > 1. Where is the share coming from? In Cloudstack, the share is
> > calculated
> > > from (CPU MHz * CPU cores).
> > > 2. How the share of a VM is mapped to the physical CPU by the
> > hypervisor?
> > > Of cause, it depends on the hypervisor implementation, but there are
> > some
> > > general rules that we need to follow, as we are living in the real
> > world:)
> > >    Rule 1: num of cpu core of a VM should be <= num of cpu core of
> > the
> > > hypervisor host. It doesn't make sense to running a 12 core VM on a
> > single
> > > core host, even some hypervisors, such as KVM, can do that.
> > Hypervisor will
> > > be busy at scheduling VCPU(the VCPU context switch is much heavier
> > than
> > > process context switch), thus bad performance for the VM.
> > >    Rule 2: The frequency of a VCPU should be <= the frequency of the
> > host
> > > hypervisor host. Can you run an one core * 12Ghz VM on a 3Ghz * 4
> > core
> > > physical CPU? Nope, in an unit time, the max freq of VCPU can get is
> > the max
> > > freq of physical cpu core, that's the physical LAW.
> > >    Rule 3: the total share of VMs <= total share of host
> > hypervisor(in case of
> > > no CPU overcommit).
> > >
> > > Currently, in cloudstack host allocator, only rule 3 is taken into
> > consideration.
> > >
> > > [1] www.cs.uiuc.edu/class/sp10/cs423/lectures/17-VMM-resource.pdf
> > > [2]
> > >
> http://www.vmware.com/pdf/vsphere4/r40/vsp_40_resource_mgmt.pdf
> > >
> > > > -----Original Message-----
> > > > From: Tamas Monos [mailto:tamasm@veber.co.uk]
> > > > Sent: Tuesday, May 22, 2012 5:41 PM
> > > > To: cloudstack-dev@incubator.apache.org
> > > > Subject: RE: Vmware CPU Cap
> > > >
> > > > Hi,
> > > >
> > > > I still don't think this is an issue as the CPU Mhz limit and the
> > > > number of cores are independent.
> > > > CPU manufacturers sell 2,4,6 cores at 3Ghz and not 6,12,18Ghz CPUs.
> > > >
> > > > So I think it is good how it works but the "number_of_cores*Mhz"
> > while
> > > > allocating should not multiply so that is the bug :) What vmware
> > does
> > > > with multiplying the cores with the core speed is bad as I can't
> > have
> > > > a 1vCPU VM at 12Ghz on a 3Ghz quad core if you know where I'm
> > coming
> > > > from....
> > > >
> > > > Regards
> > > >
> > > > -----Original Message-----
> > > > From: Tamas Monos [mailto:tamasm@veber.co.uk]
> > > > Sent: 23 May 2012 01:27
> > > > To: cloudstack-dev@incubator.apache.org
> > > > Subject: RE: Vmware CPU Cap
> > > >
> > > > Hi,
> > > >
> > > > I have confused myself too because if I have a look the database
> > and
> > > > dump the service_offerings table the limit for me is set to
> > > > 2000,3000,4000 and not 1000.
> > > > So a Mhz limit set to 4000 and 4 cores will end up as a quad core
> > box
> > > > at 4Ghz. I remember now I had to set CPU overprovisioning to 4 as
> > > > CloudStack took away 4x4Ghz=16Ghz of the available CPU.
> > > > So Cloudstack sets the VM CPU Mhz limit what the actual limit is
> > set
> > > > to in the offering but does not multiply the Mhz limit by the
> > number
> > > > of cores when setting the limit on vmware. However takes away
> > > > "number_of_cores*Mhz limit" from the available CPU capacity when
> > > > allocating.
> > > >
> > > > I'm getting confused myself so I'm not sure if this is bug now or
> > not
> > > > either :) I'm using 3.0.3
> > > >
> > > > Regards
> > > >
> > > > -----Original Message-----
> > > > From: Edison Su [mailto:Edison.su@citrix.com]
> > > > Sent: 23 May 2012 00:32
> > > > To: cloudstack-dev@incubator.apache.org; Tamas Monos
> > > > Subject: RE: Vmware CPU Cap
> > > >
> > > > But in Diego'case, the limit is set as 1000Mhz, while his service
> > > > offering is 1000Mhz * 2 cores.
> > > > Which version of cloudstack are you using? Maybe it's a regression.
> > > >
> > > > > -----Original Message-----
> > > > > From: Tamas Monos [mailto:tamasm@veber.co.uk]
> > > > > Sent: Tuesday, May 22, 2012 4:26 PM
> > > > > To: cloudstack-dev@incubator.apache.org
> > > > > Subject: RE: Vmware CPU Cap
> > > > >
> > > > > Hi,
> > > > >
> > > > > I have a service offering with 1000Mhz limit and 4 cpu cores.
> > That
> > > > > sums up to 4000Mhz.
> > > > > Cloudstack sets the limit to 4Ghz on the virtual machine and
> > > > > when
> > I
> > > > > put load on it vmware balances the load between the 4 cores
> > allowing
> > > > > them to use 1000Mhz each.
> > > > > I do not see any bugs here.
> > > > >
> > > > > Apologies if the "meant per CPU core" was incorrect. What I
> > > > > meant
> > is
> > > > > described above.
> > > > >
> > > > > Regards
> > > > >
> > > > > -----Original Message-----
> > > > > From: Edison Su [mailto:Edison.su@citrix.com]
> > > > > Sent: 23 May 2012 00:05
> > > > > To: cloudstack-dev@incubator.apache.org
> > > > > Subject: RE: Vmware CPU Cap
> > > > >
> > > > > Nope, from the document, the limit is set on whole vm:
> > > > > CPU Limits
> > > > >
> > > > > When a CPU Limit is set on a virtual machine resource settings,
> > the
> > > > > virtual machine is deliberately held from being scheduled to a
> > PCPU
> > > > > when it has used up its allocated CPU resource. This happens
> > > > > regardless of the CPU utilization. If the limit is set to
> > > > > 500MHz, the virtual machine is descheduled from the PCPU and has
> > > > > to wait before
> > > > it
> > > > > is allowed to be scheduled again. As such, the virtual machine
> > might
> > > > > experience performance degradation.
> > > > >
> > > > > Note: For an SMP virtual machine, the sum of all vCPUs cannot
> > exceed
> > > > > the specified limit. For example, 4 vCPU virtual machine with a
> > > > > limit of 1200MHz and equal load among vCPUs would result in a
> > > > > max
> > of
> > > > > 300MHz per vCPU.
> > > > >
> > > > >
> > > >
> > >
> http://kb.vmware.com/selfservice/documentLinkInt.do?micrositeID=&pop
> > > u
> > > p
> > > > > =
> > > > > true&languageId=&externalID=1033115
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Tamas Monos [mailto:tamasm@veber.co.uk]
> > > > > > Sent: Tuesday, May 22, 2012 3:43 PM
> > > > > > To: cloudstack-dev@incubator.apache.org
> > > > > > Subject: RE: Vmware CPU Cap
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > No I don't think this is a bug. When you set 1000Mhz as CPU
> > > > > > cap
> > > > that
> > > > > > is meant per core. vmWare will limit each CPU core to 1000Mhz.
> > > > > > As you gave 2 CPU cores that is 2000Mhz effective. That is how
> > > > > > vmware works.
> > > > > >
> > > > > > I have setup my offerings all to 1000Mhz as speed and just
> > > > > > increasing the number of cores.
> > > > > > 1 core ends up being 1x1000Mhz
> > > > > > 2 core ends up being 2x1000Mhz=2000Mhz ...
> > > > > > ...
> > > > > >
> > > > > > I'm actually using it in production and works quite well as
> > > > > Cloudstack
> > > > > > "allocates" 4000Mhz when I'm using 4x1000Mhz cores and vmware
> > > > > cleverly
> > > > > > balances between the cores as you put load on it and not
> > letting
> > > > any
> > > > > > of the cores above the set limit of 1000Mhz.
> > > > > >
> > > > > >
> > > > > > Regards
> > > > > >
> > > > > > -----Original Message-----
> > > > > > From: Diego Spinola Castro [mailto:spinolacastro@gmail.com]
> > > > > > Sent: 22 May 2012 19:34
> > > > > > To: cloudstack-dev@incubator.apache.org
> > > > > > Subject: Re: Vmware CPU Cap
> > > > > >
> > > > > > I forgot the link:
> > > > > > http://imageshack.us/photo/my-images/848/cpulimit.png/
> > > > > >
> > > > > > 2012/5/22 Diego Spinola Castro <spinolacastro@gmail.com>
> > > > > >
> > > > > > > I believe that is a bug with cpu cap and vmware.
> > > > > > >
> > > > > > > To reproduce:
> > > > > > >
> > > > > > > Create a offering with 2 cores and 1000mhz.
> > > > > > > Enable CPU CAP.
> > > > > > >
> > > > > > > After created instance , cs create a vm with 2 cores and
> > 1000mhz
> > > > > > > of
> > > > > > limit.
> > > > > > >
> > > > > > > I don't know for sure if is a bug, but vmware gives 1000mhz
> > > > shared
> > > > > > > with cores.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Diego
> > > > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > >


Mime
View raw message