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Re: [libvirt] [v4 0/9] Support cache tune in libvirt



On Fri, Feb 10, 2017 at 02:42:04PM +0800, Eli Qiao wrote:
> Addressed comment from v3 -> v4:
> 
> Daniel & Marcelo:
>        * Added concurrence support
> 
> Addressed comment from v2 -> v3:
> 
> Daniel:
>       * Fixed coding style, passed `make check` and `make syntax-check`
> 
>       * Variables renaming and move from header file to c file.
> 
>       * For locking/mutex support, no progress.
> 
>       There are some discussion from mailing list, but I can not find a better
>       way to add locking support without performance impact.
> 
>       I'll explain the process and please help to advice what shoud we do.
> 
>       VM create:
>       1) Get the cache left value on each bank of the host. This should be
>          shared amount all VMs.
>       2) Calculate the schemata on the bank based on all created resctrl
>          domain's schemata
>       3) Calculate the default schemata by scaning all domain's schemata.
>       4) Flush default schemata to /sys/fs/resctrl/schemata
> 
>       VM destroy:
>       1) Remove the resctrl domain of that VM
>       2) Recalculate default schemata
>       3) Flush default schemata to /sys/fs/resctrl/schemata
> 
>       The key point is that all VMs shares /sys/fs/resctrl/schemata, and
>       when a VM create a resctrl domain, the schemata of that VM depends on
>       the default schemata and all other exsited schematas. So a global
>       mutex is reqired.
> 
>       Before calculate a schemata or update default schemata, libvirt
>       should gain this global mutex.
> 
>       I will try to think more about how to support this gracefully in next
>       patch set.
> 
> Marcelo:
>       * Added vcpu support for cachetune, this will allow user to define which
>         vcpu using which cache allocation bank.
> 
>         <cachetune id='0' host_id=0 size='3072' unit='KiB' vcpus='0,1'/>
> 
>         vcpus is a cpumap, the vcpu pids will be added to tasks file

Working as expected.

>       * Added cdp compatible, user can specify l3 cache even host enable cdp.
>         See patch 8.
>         On a cdp enabled host, specify l3code/l3data by
> 
>         <cachetune id='0' host_id='0' type='l3' size='3072' unit='KiB'/>
> 
>         This will create a schemata like:
>             L3data:0=0xff00;...
>             L3code:0=0xff00;...
> 
>       * Would you please help to test if the functions work.

Setting up CDP machine.

Unrelated:

Found a bug:

The code should scan for all directories in resctrlfs,
and then find free CBM space from that:


        free_cbm_space = ~(resctrldir1.CBM_bits &
                           resctrldir2.CBM_bits &
                           ...
                           resctrldirN.CBM_bits)

        For all resctrlfs directories.

The bug is as follows:

Create a directory in resctrlfs by hand:

# mkdir newres
# cd newres
# echo "L3:0=3;1=f0000" > schemata
# virsh start guest
# cd ../b4c270b5-e0f9-4106-a446-69032872ed7e
# cat schemata
L3:0=3;1=f0000

That is, it is using the same CBM space as the "newres"
reservation.


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