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

Eli Qiao
Sent with Sparrow

On Friday, 10 February 2017 at 10:19 PM, Marcelo Tosatti wrote:

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:

* 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.

* 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:

* Would you please help to test if the functions work.

Setting up CDP machine.


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 &

For all resctrlfs directories.

The bug is as follows:

Create a directory in resctrlfs by hand:

# mkdir newres

Libvirt will not aware this after it starts running, so we should not allow operate /sys/fs/.

we will scan for all directors while the libvirt daemon begin running, and libvirt will remove exist directories if no tasks inside of it. 

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

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

As user create a new directory after libvirt running, it don’t notice newly created directory under /sys/fs/resctrl.

That will lead mess, this should be forbidden.

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