[libvirt] [PATCH 7/9] perf: add page_faults_maj software perf event support

Nitesh Konkar niteshkonkar.libvirt at gmail.com
Thu Feb 16 12:57:12 UTC 2017


On Mon, Feb 13, 2017 at 8:14 PM, John Ferlan <jferlan at redhat.com> wrote:

>
>
> On 02/13/2017 01:49 AM, Nitesh Konkar wrote:
> >
> >
> >
> > On Fri, Feb 10, 2017 at 3:22 AM, John Ferlan <jferlan at redhat.com
> > <mailto:jferlan at redhat.com>> wrote:
> >
> >
> >
> >     On 01/27/2017 06:01 AM, Nitesh Konkar wrote:
> >     > This patch adds support and documentation
> >     > for the page_faults_maj perf event.
> >     >
> >     > Signed-off-by: Nitesh Konkar <nitkon12 at linux.vnet.ibm.com <mailto:
> nitkon12 at linux.vnet.ibm.com>>
> >     > ---
> >     >  docs/formatdomain.html.in <http://formatdomain.html.in>
> >      |  7 +++++++
> >     >  docs/news.xml                               |  4 ++--
> >     >  docs/schemas/domaincommon.rng               |  1 +
> >     >  include/libvirt/libvirt-domain.h            | 10 ++++++++++
> >     >  src/libvirt-domain.c                        |  3 +++
> >     >  src/qemu/qemu_driver.c                      |  1 +
> >     >  src/util/virperf.c                          |  5 ++++-
> >     >  src/util/virperf.h                          |  1 +
> >     >  tests/genericxml2xmlindata/generic-perf.xml |  1 +
> >     >  tools/virsh.pod                             |  5 +++++
> >     >  10 files changed, 35 insertions(+), 3 deletions(-)
> >     >
> >
> >     NB: Similar comments from the page_faults_min...
> >
> >     > diff --git a/docs/formatdomain.html.in <
> http://formatdomain.html.in>
> >     b/docs/formatdomain.html.in <http://formatdomain.html.in>
> >     > index 1857168..50a6bdb 100644
> >     > --- a/docs/formatdomain.html.in <http://formatdomain.html.in>
> >     > +++ b/docs/formatdomain.html.in <http://formatdomain.html.in>
> >     > @@ -1943,6 +1943,7 @@
> >     >    <event name='context_switches' enabled='no'/>
> >     >    <event name='cpu_migrations' enabled='no'/>
> >     >    <event name='page_faults_min' enabled='no'/>
> >     > +  <event name='page_faults_maj' enabled='no'/>
> >     >  </perf>
> >     >  ...
> >     >  </pre>
> >     > @@ -2052,6 +2053,12 @@
> >     >            platform</td>
> >     >        <td><code>perf.page_faults_min</code></td>
> >     >      </tr>
> >     > +    <tr>
> >     > +      <td><code>page_faults_maj</code></td>
> >     > +      <td>the count of major page faults by applications running
> on the
> >     > +          platform</td>
> >     > +      <td><code>perf.page_faults_maj</code></td>
> >     > +    </tr>
> >
> >     As already noted in patch 3... is maj+min the same as what patch 3
> >     provides?
> >
> >
> > maj+min is not always exactly the same as page faults. Sometimes there
> > is a small offset
> > value.
> >
> > Eg: perf record -a --event={page-faults,major-faults,minor-faults}
> > 47
> > page-faults
> >
> > 0
> > major-faults
> >
> > 46 minor-faults
> > Offset by 1
> >
> > Eg:  virsh domstats --perf
> > Domain: 'Fedora'
> >   perf.page_faults=890
> >   perf.page_faults_min=890
> >   perf.page_faults_maj=0
> > Here maj+min=page_faults
> >
> >     Thus are all necessary?
> >
> > I am not sure on this part. Probably yes as we dont want
> > the user to add min+maj to get (approx)total page faults.
> >
> >
>
> I don't mind all 3 being present... still if I'm going to ask the
> question, then someone getting the stats will ask the question... they
> may also wonder why maj+min != total.
>
> Perhaps something you could dig deeper on with the kernel code
> descriptions that are setting the value.
>
> My assumption is it's the "time" of the sample. That is a total page
> fault could have been counted even though it hadn't been counted as a
> maj or min page fault.
>

I looked into the kernel code in /arch/x86/mm/fault.c and also confirmed
from
the #perf IRC that maj+min != total is valid. This is because not all
page faults fall in maj/min category. Some maybe invalid page
faults(invalid address generated)
whereas some pagefaults after occuring are not serviced due to lock
contention
so as to avoid a deadlock at that instance, thus being counted in total but
not in min/maj faults.

Also, shd i follow the comment pattern as shown
in ur patch under review, in /virsh.pod ?

Thnx.


John
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20170216/1233c307/attachment-0001.htm>


More information about the libvir-list mailing list