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

[Nitesh Konkar <niteshkonkar.libvirt@xxxxxxxxx>]

On Fri, Feb 10, 2017 at 3:22 AM, John Ferlan <jferlan@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> ---
>  docs/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 b/docs/formatdomain.html.in
> index 1857168..50a6bdb 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -1943,6 +1943,7 @@
>    &lt;event name='context_switches' enabled='no'/&gt;
>    &lt;event name='cpu_migrations' enabled='no'/&gt;
>    &lt;event name='page_faults_min' enabled='no'/&gt;
> +  &lt;event name='page_faults_maj' enabled='no'/&gt;
>  &lt;/perf&gt;
>  ...
>  </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.
 

>    </table>
>
>      <h3><a name="elementsDevices">Devices</a></h3>
> diff --git a/docs/news.xml b/docs/news.xml
> index 0e7c0d2..fe533f2 100644
> --- a/docs/news.xml
> +++ b/docs/news.xml
> @@ -138,8 +138,8 @@
>            executed, branch misses, bus cycles, stalled frontend
>            cpu cycles, stalled backend cpu cycles, ref cpu cycles,
>            cpu clock, task clock, page faults, context switches,
> -          cpu migrations and page faults min by applications
> -          running on the platform.
> +          cpu migrations, page faults min and page faults maj by
> +          applications running on the platform.

Remove news.xml

>          </description>
>        </change>
>        <change>
> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
> index f30ec0d..5f986d6 100644
> --- a/docs/schemas/domaincommon.rng
> +++ b/docs/schemas/domaincommon.rng
> @@ -439,6 +439,7 @@
>                <value>context_switches</value>
>                <value>cpu_migrations</value>
>                <value>page_faults_min</value>
> +              <value>page_faults_maj</value>
>              </choice>
>            </attribute>
>            <attribute name="enabled">
> diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
> index 108591a..d16200f 100644
> --- a/include/libvirt/libvirt-domain.h
> +++ b/include/libvirt/libvirt-domain.h
> @@ -2248,6 +2248,16 @@ void virDomainStatsRecordListFree(virDomainStatsRecordPtr *stats);
>   */
>  # define VIR_PERF_PARAM_PAGE_FAULTS_MIN  "page_faults_min"
>
> +/**
> + * VIR_PERF_PARAM_PAGE_FAULTS_MAJ:
> + *
> + * Macro for typed parameter name that represents page_faults_maj
> + * perf event which can be used to measure the count of major page
> + * faults by applications running on the platform. It corresponds
> + * to the "perf.page_faults_maj" field in the *Stats APIs.
> + */
> +# define VIR_PERF_PARAM_PAGE_FAULTS_MAJ  "page_faults_maj"
> +
>  int virDomainGetPerfEvents(virDomainPtr dom,
>                             virTypedParameterPtr *params,
>                             int *nparams,
> diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
> index 1be385e..1d7c181 100644
> --- a/src/libvirt-domain.c
> +++ b/src/libvirt-domain.c
> @@ -11265,6 +11265,9 @@ virConnectGetDomainCapabilities(virConnectPtr conn,
>   *     "perf.page_faults_min" - The count of minor page faults as unsigned long
>   *                              long. It is produced by the page_faults_min
>   *                              perf event.
> + *     "perf.page_faults_maj" - The count of major page faults as unsigned long
> + *                              long. It is produced by the page_faults_maj
> + *                              perf event
>   *
>   * Note that entire stats groups or individual stat fields may be missing from
>   * the output in case they are not supported by the given hypervisor, are not
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 4f24fa6..c88bf5a 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -9555,6 +9555,7 @@ qemuDomainSetPerfEvents(virDomainPtr dom,
>                                 VIR_PERF_PARAM_CONTEXT_SWITCHES, VIR_TYPED_PARAM_BOOLEAN,
>                                 VIR_PERF_PARAM_CPU_MIGRATIONS, VIR_TYPED_PARAM_BOOLEAN,
>                                 VIR_PERF_PARAM_PAGE_FAULTS_MIN, VIR_TYPED_PARAM_BOOLEAN,
> +                               VIR_PERF_PARAM_PAGE_FAULTS_MAJ, VIR_TYPED_PARAM_BOOLEAN,
>                                 NULL) < 0)
>          return -1;
>
> diff --git a/src/util/virperf.c b/src/util/virperf.c
> index c839b04..37f61e2 100644
> --- a/src/util/virperf.c
> +++ b/src/util/virperf.c
> @@ -46,7 +46,7 @@ VIR_ENUM_IMPL(virPerfEvent, VIR_PERF_EVENT_LAST,
>                "stalled_cycles_backend", "ref_cpu_cycles",
>                "cpu_clock", "task_clock", "page_faults",
>                "context_switches", "cpu_migrations",
> -              "page_faults_min");
> +              "page_faults_min", "page_faults_maj");
>
>  struct virPerfEvent {
>      int type;
> @@ -133,6 +133,9 @@ static struct virPerfEventAttr attrs[] = {
>      {.type = VIR_PERF_EVENT_PAGE_FAULTS_MIN,
>       .attrType = PERF_TYPE_SOFTWARE,
>       .attrConfig = PERF_COUNT_SW_PAGE_FAULTS_MIN},
> +    {.type = VIR_PERF_EVENT_PAGE_FAULTS_MAJ,
> +     .attrType = PERF_TYPE_SOFTWARE,
> +     .attrConfig = PERF_COUNT_SW_PAGE_FAULTS_MAJ},
>  };
>  typedef struct virPerfEventAttr *virPerfEventAttrPtr;
>
> diff --git a/src/util/virperf.h b/src/util/virperf.h
> index aec352b..e99c870 100644
> --- a/src/util/virperf.h
> +++ b/src/util/virperf.h
> @@ -53,6 +53,7 @@ typedef enum {
>      VIR_PERF_EVENT_CONTEXT_SWITCHES,   /* Count of context switches */
>      VIR_PERF_EVENT_CPU_MIGRATIONS,   /* Count of cpu migrations */
>      VIR_PERF_EVENT_PAGE_FAULTS_MIN,   /* Count of minor page faults */
> +    VIR_PERF_EVENT_PAGE_FAULTS_MAJ,   /* Count of major page faults */
>
>      VIR_PERF_EVENT_LAST
>  } virPerfEventType;
> diff --git a/tests/genericxml2xmlindata/generic-perf.xml b/tests/genericxml2xmlindata/generic-perf.xml
> index 62ad973..a5b6dfb 100644
> --- a/tests/genericxml2xmlindata/generic-perf.xml
> +++ b/tests/genericxml2xmlindata/generic-perf.xml
> @@ -32,6 +32,7 @@
>      <event name='context_switches' enabled='yes'/>
>      <event name='cpu_migrations' enabled='yes'/>
>      <event name='page_faults_min' enabled='yes'/>
> +    <event name='page_faults_maj' enabled='yes'/>
>    </perf>
>    <devices>
>    </devices>
> diff --git a/tools/virsh.pod b/tools/virsh.pod
> index 4eb689e..d6bec4d 100644
> --- a/tools/virsh.pod
> +++ b/tools/virsh.pod
> @@ -952,6 +952,7 @@ I<--perf> returns the statistics of all enabled perf events:
>  "perf.context_switches" - the count of context switches
>  "perf.cpu_migrations" - the count of cpu migrations
>  "perf.page_faults_min" - the count of minor page faults
> +"perf.page_faults_maj" - the count of major page faults
>
>  See the B<perf> command for more details about each event.
>
> @@ -2331,6 +2332,10 @@ B<Valid perf event names>
>                      the page was present in the page cache, and therefore the
>                      fault avoided loading it from storage, by applications
>                      running on the platform
> +  page_faults_maj - Provides the count of major page faults, that is, where
> +                    the page was not present in the page cache, and therefore
> +                    had to be fetched from storage, by applications
> +                    running on the platform

The min/maj descriptions here are a bit more wordy. It does help, but I
wonder now is this the wrong place. That is should the longer
description be in the API so that the rendered API docs get a nice long
description and the virsh output remains somewhat terse.

It really is up to you to decide, but I'm leaning towards better API doc
descriptions...

Okay. Lets have a longer description in API and terse decription in virsh output.

John

>
>  B<Note>: The statistics can be retrieved using the B<domstats> command using
>  the I<--perf> flag.
>

Thanks for all the review comments. 

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