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Re: [libvirt] [PATCHv7 00/18] Introduce x86 Cache Monitoring Technology (CMT)

On 11/6/2018 4:19 AM, John Ferlan wrote:

On 10/22/18 4:01 AM, Wang Huaqiang wrote:
This series of patches and the series already been merged introduce
the x86 Cache Monitoring Technology (CMT) to libvirt by interacting
with kernel resource control (resctrl) interface. CMT is one of the
Intel(R) x86 CPU feature which belongs to the Resource Director
Technology (RDT). CMT reports the occupancy of the last level cache,
which is shared by all CPU cores.

Rather than top or bottom post ;-) - as noted during the reviewing -
many of the patches are fine; however, once we get to the meat in patch
12 and beyond I think more adjustment is necessary. I wouldn't want to
introduce the XML from patch 12, but have no teeth behind it from the
remaining patches.

Really appreciate your review and comments, your comments not only pointed out
my faults but also provide very reasonable suggestions.

For patch 1-11, I also addressed your review opinions in my next version code, please
make a review at your convenient time.

For patches after 11, I also addressed your review suggestions by removing the patches for adding 'resctrl->id' and for 'virResctrlMonitorIsRunning', and made some code split
for patch17.  Please make a review.

Getting closer, but not quite there yet.  If you're good with my
proposed adjustments for patches 1-11, then I can get those pushed so
that we can make some progress.

On your next round, please let's try to get a news.xml to summarize the
changes added at the end. Saves me from chasing later on.

OK. A separate patch for change of news.xml is appended.

I won't have a lot of cycles for the rest of the week to debate or
provide feedback. I'm in class Wed -> Fri.  I really don't think the
comments I've provided in the later patches are that controversial.

Agree. Your comments are very accurate. This time I have time to prepare the code along with
the reply to your review emails.

I do think we probably need a way to handle the Unplug with the existing
usage of the *tasks file before we go too far and add monitor.

By analyzing the code handling vcpu unplug , it seems there is no problem to keep the *tasks file aligned with PIDs. Because the removal of PID is automatically done by
kernel if kernel find some vcpu process is disappeared.

I need more time to test on vcpu unplug cases for my code. I have not achieved a successful live
removal of vcpus, even with code without my new resctrl monitor patches.

I will update when I have some conclusion.

  You also
need to figure a way to not add the same pid twice. I realize now that a
*Remove operation will remove the *tasks file from a $path so some
concerns I had were at least reduced.

To add PID twice is because I thought the *tasks file could be removed/added in process of re-connection, when performing 'systemctl restart libvirtd',  but it seems is does not.

So it is not necessary to add same pid twice. The libvirtd daemon restart process works fine
after the remove of relevant patch.

And *tasks file is not removed or changed in process of re-connection. So patch18 and patch14
are removed.


Thanks for all for your review.

In the v1 series, an original and complete feature for CMT was introduced
The v2 and v3 patches address the feature for the host capability of CMT.
v4 is addressing the feature for monitoring VM vcpu thread set cache
occupancy and reporting it through a virsh command.

We have serval discussion about the enabling of CMT, please refer to
following links for the RFCs.

And the merged commits are list as below, for host capability of CMT.

1. About reason why CMT is necessary in libvirt?
The perf events of 'CMT, MBML, MBMT' have been phased out since Linux
kernel commit c39a0e2c8850f08249383f2425dbd8dbe4baad69, in libvirt
the perf based cmt,mbm will not work with the latest linux kernel. These
patches add CMT feature to libvirt through kernel resctrlfs interface.

2 Create cache monitoring group (cache monitor).

     The main interface for creating monitoring group is through XML file. The
proposed configuration is like:

         <cachetune vcpus='1'>
           <cache id='0' level='3' type='code' size='7680' unit='KiB'/>
           <cache id='1' level='3' type='data' size='3840' unit='KiB'/>
     +     <monitor level='3' vcpus='1'/>
         <cachetune vcpus='4-7'>
     +     <monitor level='3' vcpus='4-6'/>

In above XML, created 2 cache resctrl allocation groups and 2 resctrl
monitoring groups.
The changes of cache monitor will be effective in next booting of VM.

2 Show CMT result through command 'domstats'

Adding the interface in qemu to report this information for resource
monitor group through command 'virsh domstats --cpu-total'.
Below is a typical output:

      # virsh domstats 1 --cpu-total
      Domain: 'ubuntu16.04-base'

Changes in v7:
- Add several lines removed by mistake.

Changes in v6:
- Addressing John's review comments for v5.
- Removed and cleaned the concepts of 'default allocation' and
'default monitor'.
- qemu: virsh domstats --cpu-total output for CMT, add identifier
'monitor' for each itm.

Changes in v5:
- qemu: Setting up vcpu and adding pids to resctrl monitor groups during
- Add the document for domain configuration related to resctrl monitor.

Changes in v4:
v4 is addressing the feature for monitoring VM vcpu
thread set cache occupancy and reporting it through a
virsh command.
- Introduced resctrl default allocation
- Introduced resctrl monitor and default monitor

Changes in v3:
- Addressed John Ferlan's review.
- Typo fixed.
- Removed VIR_ENUM_DECL(virMonitor);

Changes in v2:
- Introduced MBM capability.
- Capability layout changed
     * Moved <monitor> from cahe <bank> to <cache>
     * Renamed <Threshold> to <reuseThreshold>
- Document for 'reuseThreshold' changed.
- Introduced API virResctrlInfoGetMonitorPrefix
- Added more tests, covering standalone CMT, fake new
- Creating CMT resource control group will be
   subsequent job.

Wang Huaqiang (18):
   docs,util: Refactor schemas and virresctrl to support optional cache
   util: Introduce resctrl monitor for CMT
   util: Refactor code for determining allocation path
   util: Add interface to determine monitor path
   util: Refactor code for adding PID to the resource group
   util: Add interface for adding PID to the monitor
   util: Refactor code for creating resctrl group
   util: Add interface for creating monitor group
   util: Add more interfaces for resctrl monitor
   conf: Remove virDomainResctrlAppend and introduce virDomainResctrlNew
   conf: move virResctrlAllocIsEmpty to a place a litter lower
   conf: Introduce cache monitor element in cachetune
   qemu: enable resctrl monitor in qemu
   util: Add function for checking if monitor is running
   conf: Add 'id' to virDomainResctrlDef
   qemu: refactor qemuDomainGetStatsCpu
   qemu: Report cache occupancy (CMT) with domstats
   qemu: Setting up vcpu and adding pids to resctrl monitor groups during

  docs/formatdomain.html.in                          |  30 +-
  docs/schemas/domaincommon.rng                      |  14 +-
  src/conf/domain_conf.c                             | 310 ++++++++++--
  src/conf/domain_conf.h                             |  12 +
  src/libvirt-domain.c                               |   9 +
  src/libvirt_private.syms                           |  11 +
  src/qemu/qemu_driver.c                             | 270 +++++++++-
  src/qemu/qemu_process.c                            |  69 ++-
  src/util/virresctrl.c                              | 560 +++++++++++++++++++--
  src/util/virresctrl.h                              |  49 ++
  tests/genericxml2xmlindata/cachetune-cdp.xml       |   3 +
  .../cachetune-colliding-monitor.xml                |  30 ++
  tests/genericxml2xmlindata/cachetune-small.xml     |   7 +
  tests/genericxml2xmltest.c                         |   2 +
  14 files changed, 1283 insertions(+), 93 deletions(-)
  create mode 100644 tests/genericxml2xmlindata/cachetune-colliding-monitor.xml

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