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From Tamas Monos <tam...@veber.co.uk>
Subject RE: Vmware CPU Cap
Date Wed, 23 May 2012 21:58:50 GMT
Hi,

Before we would touch that rule 2:
While utilizing 12Ghz on a single core is not possible it is possible to have effective 12Ghz
on 4 cores at 3Ghz via parallel processing.
If I start 4 cpuburn threads on a quad core it will use all four 3Ghz cores flat out "giving
similar speed as 1 core@12Ghz would be"*. As vmware uses the limit parameter as limit to the
whole CPU utilization rule 2 approach would prevent me effectively utilizing the CPU on vmware
because if we say the CPU speed in Mhz cannot be larger than the core speed I would be limited
to an effective speed of core-speed/number_of_cores. This would mean  3000/4=750Mhz per core
on a 4vCPU VM. If you set "core_number*core_speed" as limit you already broke rule 2 as the
CPU is set higher than its core speed.

I believe it good as it is now.

Regards

-----Original Message-----
From: Prachi Damle [mailto:Prachi.Damle@citrix.com] 
Sent: 23 May 2012 22:36
To: cloudstack-dev@incubator.apache.org
Subject: RE: Vmware CPU Cap

Yeah, rule#1 and #3 are considered by the current Host Allocator; rule#2 to compare just the
speed is missing.

Prachi

-----Original Message-----
From: Anthony Xu [mailto:Xuefei.Xu@citrix.com]
Sent: Wednesday, May 23, 2012 2:06 PM
To: cloudstack-dev@incubator.apache.org
Subject: RE: Vmware CPU Cap

Checked the code, I think we miss rule 2 in allocator.

Anthony

> -----Original Message-----
> From: Anthony Xu [mailto:Xuefei.Xu@citrix.com]
> Sent: Wednesday, May 23, 2012 1:50 PM
> To: cloudstack-dev@incubator.apache.org
> Subject: RE: Vmware CPU Cap
> 
> I'm pretty sure we have that before we redesign allocator.
> 
> Anthony
> 
> > -----Original Message-----
> > From: Alex Huang [mailto:Alex.Huang@citrix.com]
> > Sent: Wednesday, May 23, 2012 1:44 PM
> > To: cloudstack-dev@incubator.apache.org
> > Subject: RE: Vmware CPU Cap
> >
> > 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
> > > > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >




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