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Re: [libvirt] [RFC v3 0/8] Support cache tune in libvirt

Eli Qiao
Sent with Sparrow

On Thursday, 9 February 2017 at 10:25 PM, Marcelo Tosatti wrote:

On Thu, Feb 09, 2017 at 03:43:01PM +0800, Eli Qiao wrote:
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

Yes, this 4 steps have to be serialized and cannot occur in parallel.

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.

There are two things you need to protect:

1) Access to the filesystem (and schematas). For this you should use
the fcntl lock as mentioned previously:

Other applications that use resctrlfs should use the same lock.

All you have to do is to grab and release the fcntl lock as follows:

+#include <sys/file.h>
+#include <stdlib.h>
+void resctrl_take_shared_lock(int fd)
+ int ret;
+ /* take shared lock on resctrl filesystem */
+ ret = flock(fd, LOCK_SH);
+ if (ret) {
+ perror("flock");
+ exit(-1);
+ }
+void resctrl_take_exclusive_lock(int fd)
+ int ret;
+ /* release lock on resctrl filesystem */
+ ret = flock(fd, LOCK_EX);
+ if (ret) {
+ perror("flock");
+ exit(-1);
+ }
+void resctrl_release_lock(int fd)
+ int ret;
+ /* take shared lock on resctrl filesystem */
+ ret = flock(fd, LOCK_UN);
+ if (ret) {
+ perror("flock");
+ exit(-1);
+ }
+void main(void)
+ int fd, ret;
+ fd = open("/sys/fs/resctrl", O_DIRECTORY);
+ if (fd == -1) {
+ perror("open");
+ exit(-1);
+ }
+ resctrl_take_shared_lock(fd);
+ /* code to read directory contents */
+ resctrl_release_lock(fd);
+ resctrl_take_exclusive_lock(fd);
+ /* code to read and write directory contents */
+ resctrl_release_lock(fd);

Thank Marcelo, libvirt have a util named virFileLock

would that be same with your flock?

2) The internal data structures in libvirt. I suppose you can
simply add a mutex to protect all of the "struct _virResCtrl"
since there should be no contention on that lock.
Sure, I will try to refine my code.

* 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

* 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'/>
rcelo amt patchesv3]$ cd ..
This will create a schemata like:

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

Will do.

* Xml test case, I have no time to work on this yet, would you please
show me an example, would like to amend it later.

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.

Can you please list the TODOs?

Sure, there‚Äôs one public API missing for query cache free on each bank. 

Some discussion about this feature support can be found from:

Eli Qiao (8):
Resctrl: Add some utils functions
Resctrl: expose cache information to capabilities
Resctrl: Add new xml element to support cache tune
Resctrl: Add private interface to set cachebanks
Qemu: Set cache banks
Resctrl: enable l3code/l3data
Resctrl: Make sure l3data/l3code are pairs
Resctrl: Compatible mode for cdp enabled

docs/schemas/domaincommon.rng | 46 ++
include/libvirt/virterror.h | 1 +
po/POTFILES.in | 1 +
src/Makefile.am | 1 +
src/conf/capabilities.c | 56 +++
src/conf/capabilities.h | 23 +
src/conf/domain_conf.c | 182 +++++++
src/conf/domain_conf.h | 19 +
src/libvirt_private.syms | 11 +
src/nodeinfo.c | 64 +++
src/nodeinfo.h | 1 +
src/qemu/qemu_capabilities.c | 8 +
src/qemu/qemu_driver.c | 6 +
src/qemu/qemu_process.c | 53 ++
src/util/virerror.c | 1 +
src/util/virresctrl.c | 1091 +++++++++++++++++++++++++++++++++++++++++
src/util/virresctrl.h | 85 ++++
17 files changed, 1649 insertions(+)
create mode 100644 src/util/virresctrl.c
create mode 100644 src/util/virresctrl.h


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