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Re: [libvirt] [resend v2 0/7] Support cache tune in libvirt



On Tue, Feb 07, 2017 at 02:43:13PM +0800, Eli Qiao wrote:
> 
> 
> --  
> Eli Qiao
> Sent with Sparrow (http://www.sparrowmailapp.com/?sig)
> 
> 
> On Tuesday, 7 February 2017 at 3:03 AM, Marcelo Tosatti wrote:
> 
> > On Mon, Feb 06, 2017 at 01:33:09PM -0200, Marcelo Tosatti wrote:
> > > On Mon, Feb 06, 2017 at 10:23:35AM +0800, Eli Qiao wrote:
> > > > This series patches are for supportting CAT featues, which also
> > > > called cache tune in libvirt.
> > > >  
> > > > First to expose cache information which could be tuned in capabilites XML.
> > > > Then add new domain xml element support to add cacahe bank which will apply
> > > > on this libvirt domain.
> > > >  
> > > > This series patches add a util file `resctrl.c/h`, an interface to talk with
> > > > linux kernel's sys fs.
> > > >  
> > > > There are still some TODOs such as expose new public interface to get free
> > > > cache information.
> > > >  
> > > > Some discussion about this feature support can be found from:
> > > > https://www.redhat.com/archives/libvir-list/2017-January/msg00644.html
> > > >  
> > >  
> > >  
> > > Two comments:
> > >  
> > > 1) Please perform appropriate filesystem locking when accessing
> > > resctrlfs, as described at:
> > >  
> > > http://www.spinics.net/lists/linux-tip-commits/msg36754.html
> 
> Sure.  
> > >  
> > > 2)  
> > >  
> > > <cachetune id='10' host_id='1' type='l3' size='3072' unit='KiB'/>
> > >  
> > > [b4c270b5-e0f9-4106-a446-69032872ed7d]# cat tasks  
> > > 8654
> > > [b4c270b5-e0f9-4106-a446-69032872ed7d]# pstree -p | grep qemu
> > > |-qemu-kvm(8654)-+-{qemu-kvm}(8688)
> > > | |-{qemu-kvm}(8692)
> > > | `-{qemu-kvm}(8693)
> > >  
> > > Should add individual vcpus to the "tasks" file, not the main QEMU
> > > process.
> > >  
> > > The NFV usecase requires exclusive CAT allocation for the vcpu which
> > > runs the sensitive workload.
> > >  
> > > Perhaps:
> > >  
> > > <cachetune id='10' host_id='1' type='l3' size='3072' unit='KiB'/>  
> > >  
> > > Adds all vcpus that are pinned to the socket which cachebank with
> > > host_id=1.
> > >  
> > > <cachetune id='10' host_id='1' type='l3' size='3072' unit='KiB' vcpus=2,3/>  
> > >  
> > > Adds PID of vcpus 2 and 3 to resctrl directory created for this
> > > allocation.
> > >  
> >  
> >  
> Hmm.. in this case, we need to figure out what’s the pid of vcpus=2 and vcpu=3 and added them to the resctrl directory.

Yes and only the pids of vcpus=2 and vcpus=3, not of any other vcpus.

> currently, I create a resctrl directory(called resctrl domain) for a VM so just put all task ids to it.
> 
> this is my though:
> 
> let say the vm has vcpus=0 1 2 3, and you want to let 0, 1 benefit cache on host_id=0, and 2, 3 on host_id=1
> 
> you will do:
> 
> 1)
>     pin vcpus 0, 1 on the cpus of socket 0  
>     pin vcpus 2, 3 on the cpus of socket 1
> this can be done in vcputune
> 
> 2) define cache tune like this:
> <cachetune id='0' host_id=‘0' type='l3' size='3072' unit='KiB'/>
> <cachetune id='1' host_id='1' type='l3' size='3072' unit='KiB'/>
> 
> in libvirt:
> we create a resctrl directory naming with the VM’s uuid
> and set schemata for each socket 0, and socket 1, put all qemu tasks ids into tasks file, this will work fine.  

No, please don't do this.

> please be note that in a resctrl directory, we can define schemata for each socket id separately.

Please do not put vcpus automatically into the reservations.
Its necessary to have certain vcpus in a reservation and some not.

For example: 2 vcpu guest, vcpu0 pinned to socket 0 cpu0, 
  		           vcpu1 pinned to socket 0 cpu1.


<cachetune id='0' host_id=‘0' type='l3' size='3072' unit='KiB'/>

We want _only_ vcpu1 to be part of this reservation, and not vcpu0 
(want vcpu0 to use the default group, ie. schemata file at 

/sys/fs/resctrl/schemata

So please have the ability to add vcpus to the XML syntax:

<cachetune id='0' host_id=‘0' type='l3' size='3072' unit='KiB'
vcpus='1'/>

or

<cachetune id='0' host_id=‘0' type='l3' size='3072' unit='KiB'
vcpus='2,3'/>

This also allows different sizes to be specified.


> > 3) CDP / non-CDP convertion.
> >  
> > In case the size determination has been performed with non-CDP,
> > to emulate such allocation on a CDP host,
> > it would be good to allow both code and data allocations to share
> > the CBM space:  
> >  
> IOM, I don’t think it’s good to have this.
> in libvirt capabilities xml, the application will get to know if the host support cdp or not.
>   
> >  
> > <cachetune id='10' host_id='1' type='l3data' size='3072' unit='KiB'/>
> > <cachetune id='10' host_id='1' type='l3code' size='3072' unit='KiB'/>
> >  
> > Perhaps if using the same ID?
> I am open to hear about what other’s say,  
>   
> >  
> >  
> > Other than that, testing looks good.  
> Thanks for the testing.  
> 
> 


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