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Re: [libvirt] [PATCH v2 05/10] Determine whether to start balloon memory stats gathering.



On 08.07.2013 21:20, John Ferlan wrote:
> At vm startup, reconnect, and attach - check for the presence of the balloon
> driver and save the path in the private area of the driver.  This path will
> remain constant throughout the life of the domain and can then be used rather
> than attempting to find the path each time balloon driver statistics are
> fetched or the collection period changes. The qom object model model requires
> setting object properties after device startup.  That is, it's not possible
> to pass the period along via the startup code as it won't be recognized.
> If a balloon driver path is found a check of the existing collection period
> will be made against the saved domain value in order to determine if an
> adjustment needs to be made to the period to start or stop collecting stats
> ---
>  src/qemu/qemu_monitor.c      | 130 +++++++++++++++++++++++++++++++++++++++++++
>  src/qemu/qemu_monitor.h      |   2 +
>  src/qemu/qemu_monitor_json.c |  42 ++++++++++++++
>  src/qemu/qemu_monitor_json.h |   3 +
>  src/qemu/qemu_process.c      |  21 ++++++-
>  5 files changed, 196 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> index fe5ab0a..038c9e8 100644
> --- a/src/qemu/qemu_monitor.c
> +++ b/src/qemu/qemu_monitor.c
> @@ -83,6 +83,9 @@ struct _qemuMonitor {
>  
>      /* cache of query-command-line-options results */
>      virJSONValuePtr options;
> +
> +    /* If found, path to the virtio memballoon driver */
> +    char *balloonpath;
>  };
>  
>  static virClassPtr qemuMonitorClass;
> @@ -248,6 +251,7 @@ static void qemuMonitorDispose(void *obj)
>      virCondDestroy(&mon->notify);
>      VIR_FREE(mon->buffer);
>      virJSONValueFree(mon->options);
> +    VIR_FREE(mon->balloonpath);
>  }
>  
>  
> @@ -929,6 +933,107 @@ qemuMonitorSetOptions(qemuMonitorPtr mon, virJSONValuePtr options)
>      mon->options = options;
>  }
>  
> +/* Search the qom objects for the balloon driver object by it's known name
> + * of "virtio-balloon-pci".  The entry for the driver will be found in the
> + * returned 'type' field using the syntax "child<virtio-balloon-pci>".
> + *
> + * Once found, check the entry to ensure it has the correct property listed.
> + * If it does not, then obtaining statistics from qemu will not be possible.
> + * This feature was added to qemu 1.5.
> + *
> + * This procedure will be call recursively until found or the qom-list is
> + * exhausted.
> + *
> + * Returns:
> + *
> + *   1  - Found
> + *   0  - Not found still looking
> + *  -1  - Error bail out
> + *
> + * NOTE: This assumes we have already called qemuDomainObjEnterMonitor()
> + */
> +static int
> +qemuMonitorFindBalloonObjectPath(qemuMonitorPtr mon,
> +                                 virDomainObjPtr vm,
> +                                 const char *curpath)
> +{
> +    int i,j;

size_t i,j, npaths = 0, nprops = 0;

> +    int npaths = 0;
> +    int nprops = 0;
> +    int ret = 0;
> +    char *nextpath = NULL;
> +    qemuMonitorJSONListPathPtr *paths = NULL;
> +    qemuMonitorJSONListPathPtr *bprops = NULL;
> +
> +    /* Not supported */
> +    if (vm->def->memballoon &&
> +        vm->def->memballoon->model != VIR_DOMAIN_MEMBALLOON_MODEL_VIRTIO) {
> +        VIR_DEBUG("Model must be virtio to get memballoon path");
> +        return -1;
> +    }
> +
> +    /* Already set and won't change */
> +    if (mon->balloonpath)
> +        return 1;
> +
> +    VIR_DEBUG("Searching for Balloon Object Path starting at %s", curpath);
> +
> +    npaths = qemuMonitorJSONGetObjectListPaths(mon, curpath, &paths);
> +
> +    for (i = 0; i < npaths && ret == 0; i++) {
> +
> +        if (STREQ_NULLABLE(paths[i]->type, "link<virtio-balloon-pci>")) {
> +            VIR_DEBUG("Path to <virtio-balloon-pci> is '%s/%s'",
> +                      curpath, paths[i]->name);
> +            if (virAsprintf(&nextpath, "%s/%s", curpath, paths[i]->name) < 0) {
> +                ret = -1;
> +                goto cleanup;
> +            }
> +
> +            /* Now look at the each of the property entries to determine
> +             * whether "guest-stats-polling-interval" exists.  If not,
> +             * then this version of qemu/kvm does not support the feature.
> +             */
> +            nprops = qemuMonitorJSONGetObjectListPaths(mon, nextpath, &bprops);
> +            for (j = 0; j < nprops; j++) {
> +                if (STREQ(bprops[j]->name, "guest-stats-polling-interval")) {
> +                    mon->balloonpath = nextpath;
> +                    nextpath = NULL;
> +                    ret = 1;
> +                    goto cleanup;

Maybe I'd add VIR_DEBUG() here to log the path.

> +                }
> +            }
> +
> +            /* If we get here, we found the path, but not the property */
> +            VIR_DEBUG("Property 'guest-stats-polling-interval' not found");
> +            ret = -1;
> +            goto cleanup;
> +        }
> +
> +        /* Type entries that begin with "child<" are a branch that can be
> +         * traversed looking for more entries
> +         */
> +        if (paths[i]->type && STRPREFIX(paths[i]->type, "child<")) {
> +            if (virAsprintf(&nextpath, "%s/%s", curpath, paths[i]->name) < 0) {
> +                virReportOOMError();
> +                ret = -1;
> +                goto cleanup;
> +            }
> +            ret = qemuMonitorFindBalloonObjectPath(mon, vm, nextpath);
> +        }
> +    }
> +
> +cleanup:
> +    for (i = 0; i < npaths; i++)
> +        qemuMonitorJSONListPathFree(paths[i]);
> +    VIR_FREE(paths);
> +    for (j = 0; j < nprops; j++)
> +        qemuMonitorJSONListPathFree(bprops[j]);
> +    VIR_FREE(bprops);
> +    VIR_FREE(nextpath);
> +    return ret;
> +}
> +
>  int qemuMonitorHMPCommandWithFd(qemuMonitorPtr mon,
>                                  const char *cmd,
>                                  int scm_fd,
> @@ -1390,6 +1495,31 @@ int qemuMonitorGetMemoryStats(qemuMonitorPtr mon,
>      return ret;
>  }
>  
> +int qemuMonitorSetMemoryStatsPeriod(qemuMonitorPtr mon,
> +                                    int period)
> +{
> +    int ret = -1;
> +    VIR_DEBUG("mon=%p period=%d", mon, period);
> +
> +    if (!mon) {
> +        virReportError(VIR_ERR_INVALID_ARG, "%s",
> +                       _("monitor must not be NULL"));
> +        return -1;
> +    }
> +
> +    if (!mon->json) {
> +        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> +                       _("JSON monitor is required"));
> +        return -1;
> +    }
> +
> +    if (qemuMonitorFindBalloonObjectPath(mon, mon->vm, "/") == 1) {
> +        ret = qemuMonitorJSONSetMemoryStatsPeriod(mon, mon->balloonpath,
> +                                                  period);
> +    }
> +    return ret;
> +}
> +
>  int
>  qemuMonitorBlockIOStatusToError(const char *status)
>  {
> diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
> index 78011ee..12b730a 100644
> --- a/src/qemu/qemu_monitor.h
> +++ b/src/qemu/qemu_monitor.h
> @@ -265,6 +265,8 @@ int qemuMonitorGetBalloonInfo(qemuMonitorPtr mon,
>  int qemuMonitorGetMemoryStats(qemuMonitorPtr mon,
>                                virDomainMemoryStatPtr stats,
>                                unsigned int nr_stats);
> +int qemuMonitorSetMemoryStatsPeriod(qemuMonitorPtr mon,
> +                                    int period);
>  
>  int qemuMonitorBlockIOStatusToError(const char *status);
>  virHashTablePtr qemuMonitorGetBlockInfo(qemuMonitorPtr mon);
> diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
> index 9487955..2d7f9b6 100644
> --- a/src/qemu/qemu_monitor_json.c
> +++ b/src/qemu/qemu_monitor_json.c
> @@ -1495,6 +1495,48 @@ cleanup:
>  }
>  
>  
> +/*
> + * Using the provided balloonpath, determine if we need to set the

s/balloonpath/balloon path/

> + * collection interval property to enable statistics gathering.
> + */
> +int
> +qemuMonitorJSONSetMemoryStatsPeriod(qemuMonitorPtr mon,
> +                                    char *balloonpath,
> +                                    int period)
> +{
> +    qemuMonitorJSONObjectProperty prop;
> +
> +    /* Get the current value of the stats polling interval */
> +    memset(&prop, 0, sizeof(qemuMonitorJSONObjectProperty));
> +    prop.type = QEMU_MONITOR_OBJECT_PROPERTY_INT;
> +    if (qemuMonitorJSONGetObjectProperty(mon, balloonpath,
> +                                         "guest-stats-polling-interval",
> +                                         &prop) < 0) {
> +        VIR_DEBUG("Failed to get polling interval for balloon driver");
> +        return 0;

Shouldn't we return -1 here? I mean, if caller requires us to set an
interval, we should error out if we fail. Why are we querying for the
interval prior setting it anyway?

> +    }
> +
> +    VIR_DEBUG("memballoon period=%d 'guest-stats-polling-interval'=%d",
> +              period,  prop.val.i);
> +
> +    /* Same value - no need to set */
> +    if (period == prop.val.i)
> +        return 0;
> +
> +    /* Set to the value in memballoon (could enable or disable) */
> +    memset(&prop, 0, sizeof(qemuMonitorJSONObjectProperty));
> +    prop.type = QEMU_MONITOR_OBJECT_PROPERTY_INT;
> +    prop.val.i = period;
> +    if (qemuMonitorJSONSetObjectProperty(mon, balloonpath,
> +                                         "guest-stats-polling-interval",
> +                                         &prop) < 0) {
> +        VIR_DEBUG("Failed to set polling interval for balloon driver");

This is unnecessary as long as qemuMonitorJSONSetObjectProperty reports
error on retval < 0, which it does.

> +        return -1;
> +    }
> +    return 0;
> +}
> +
> +
>  int qemuMonitorJSONGetBlockInfo(qemuMonitorPtr mon,
>                                  virHashTablePtr table)
>  {
> diff --git a/src/qemu/qemu_monitor_json.h b/src/qemu/qemu_monitor_json.h
> index fd0dedd..b0068ff 100644
> --- a/src/qemu/qemu_monitor_json.h
> +++ b/src/qemu/qemu_monitor_json.h
> @@ -61,6 +61,9 @@ int qemuMonitorJSONGetBalloonInfo(qemuMonitorPtr mon,
>  int qemuMonitorJSONGetMemoryStats(qemuMonitorPtr mon,
>                                    virDomainMemoryStatPtr stats,
>                                    unsigned int nr_stats);
> +int qemuMonitorJSONSetMemoryStatsPeriod(qemuMonitorPtr mon,
> +                                        char *balloonpath,
> +                                        int period);
>  int qemuMonitorJSONGetBlockInfo(qemuMonitorPtr mon,
>                                  virHashTablePtr table);
>  int qemuMonitorJSONGetBlockStatsInfo(qemuMonitorPtr mon,
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index f8c652f..fd3b7a8 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -3091,6 +3091,13 @@ qemuProcessReconnect(void *opaque)
>      if (qemuProcessRecoverJob(driver, obj, conn, &oldjob) < 0)
>          goto error;
>  
> +    if (obj->def->memballoon) {
> +        qemuDomainObjEnterMonitor(driver, obj);
> +        qemuMonitorSetMemoryStatsPeriod(priv->mon,
> +                                        obj->def->memballoon->period);
> +        qemuDomainObjExitMonitor(driver, obj);
> +    }
> +

Why do we want to enable this on ProcessReconnect?

>      /* update domain state XML with possibly updated state in virDomainObj */
>      if (virDomainSaveStatus(driver->xmlopt, cfg->stateDir, obj) < 0)
>          goto error;
> @@ -3910,6 +3917,9 @@ int qemuProcessStart(virConnectPtr conn,
>          goto cleanup;
>      }
>      qemuDomainObjEnterMonitor(driver, vm);
> +    if (vm->def->memballoon)
> +        qemuMonitorSetMemoryStatsPeriod(priv->mon,
> +                                        vm->def->memballoon->period);

It makes sense here.

>      if (qemuMonitorSetBalloon(priv->mon, cur_balloon) < 0) {
>          qemuDomainObjExitMonitor(driver, vm);
>          goto cleanup;
> @@ -4439,11 +4449,18 @@ int qemuProcessAttach(virConnectPtr conn ATTRIBUTE_UNUSED,
>      if (!virDomainObjIsActive(vm))
>          goto cleanup;
>  
> -    if (running)
> +    if (running) {
>          virDomainObjSetState(vm, VIR_DOMAIN_RUNNING,
>                               VIR_DOMAIN_RUNNING_UNPAUSED);
> -    else
> +        if (vm->def->memballoon) {
> +            qemuDomainObjEnterMonitor(driver, vm);
> +            qemuMonitorSetMemoryStatsPeriod(priv->mon,
> +                                            vm->def->memballoon->period);
> +            qemuDomainObjExitMonitor(driver, vm);
> +        }
> +    } else {
>          virDomainObjSetState(vm, VIR_DOMAIN_PAUSED, reason);
> +    }
>  
>      VIR_DEBUG("Writing domain status to disk");
>      if (virDomainSaveStatus(driver->xmlopt, cfg->stateDir, vm) < 0)
> 

Michal


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