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[libvirt] [PATCH 1/4] networkAllocateActualDevice: Set QoS for bridgeless networks too



https://bugzilla.redhat.com/show_bug.cgi?id=1055484

Currently, libvirt's XML schema of network allows QoS to be defined for
every network even though it has no bridge. For instance:

<network>
    <name>vdsm-no-bridge</name>
    <forward mode='passthrough'>
      <interface dev='em1.10'/>
    </forward>
    <bandwidth>
        <inbound average='1000' peak='5000' burst='1024'/>
        <outbound average='1000' burst='1024'/>
    </bandwidth>
</network>

The bandwidth limitations can be, however, applied even on such
networks. In fact, they are gonna be applied on the interface that will
be connected to the network on a domain startup. This approach, however,
has one limitation. With bridged networks, there are two points where
QoS can be set: bridge and domain interface. The lower limit of the two
is enforced then. For instance, if the interface has 10Mbps average, but
the network only 1Mbps, there's no way for interface to transmit packets
faster than the 1Mbps limit. With two points this is enforced by kernel.
With only one point, we must combine both QoS settings into one which is
set afterwards. Look at virNetDevBandwidthMinimal() and you'll
understand immediately what I mean.

Signed-off-by: Michal Privoznik <mprivozn redhat com>
---
 src/libvirt_private.syms      |  1 +
 src/network/bridge_driver.c   | 25 +++++++++++-
 src/util/virnetdevbandwidth.c | 88 +++++++++++++++++++++++++++++++++++++++++++
 src/util/virnetdevbandwidth.h |  6 +++
 4 files changed, 118 insertions(+), 2 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 13caf93..0c16343 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1469,6 +1469,7 @@ virNetDevBandwidthClear;
 virNetDevBandwidthCopy;
 virNetDevBandwidthEqual;
 virNetDevBandwidthFree;
+virNetDevBandwidthMinimal;
 virNetDevBandwidthPlug;
 virNetDevBandwidthSet;
 virNetDevBandwidthUnplug;
diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 0b43a67..904aad5 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -3284,9 +3284,30 @@ networkAllocateActualDevice(virDomainNetDefPtr iface)
     else if (portgroup && portgroup->bandwidth)
         bandwidth = portgroup->bandwidth;
 
-    if (bandwidth && virNetDevBandwidthCopy(&iface->data.network.actual->bandwidth,
-                                            bandwidth) < 0)
+    /* For a bridgeless networks we must take into account any QoS set to them.
+     * This is, however, a bit tricky. With bridged network there are two
+     * points where QoS can be set: domain's interface and the bridge. The
+     * limits on those differ (in general) in which case the lower limit gets
+     * into effect. For example, if domain's interface average is 10Mbps but
+     * the network's is just 1Mbps, the domain will not be able to send data
+     * any faster than 1Mbps. However, on bridgeless networks we can't just set
+     * those two points and let kernel do its job since we have only single
+     * point. Therefore, we must combine the QoS settings from both domain's
+     * interface and network and choose the minimal value from pairs.
+     */
+    if (netdef->forward.type == VIR_NETWORK_FORWARD_PRIVATE ||
+        netdef->forward.type == VIR_NETWORK_FORWARD_VEPA ||
+        netdef->forward.type == VIR_NETWORK_FORWARD_PASSTHROUGH ||
+        netdef->forward.type == VIR_NETWORK_FORWARD_HOSTDEV) {
+        if (virNetDevBandwidthMinimal(&iface->data.network.actual->bandwidth,
+                                      bandwidth,
+                                      netdef->bandwidth) < 0)
+            goto error;
+    } else if (bandwidth &&
+               virNetDevBandwidthCopy(&iface->data.network.actual->bandwidth,
+                                      bandwidth) < 0) {
         goto error;
+    }
 
     /* copy appropriate vlan info to actualNet */
     if (iface->vlan.nTags > 0)
diff --git a/src/util/virnetdevbandwidth.c b/src/util/virnetdevbandwidth.c
index ed6a19d..05f3d6e 100644
--- a/src/util/virnetdevbandwidth.c
+++ b/src/util/virnetdevbandwidth.c
@@ -27,6 +27,7 @@
 #include "viralloc.h"
 #include "virerror.h"
 #include "virstring.h"
+#include "virutil.h"
 
 #define VIR_FROM_THIS VIR_FROM_NONE
 
@@ -588,3 +589,90 @@ cleanup:
     VIR_FREE(ceil);
     return ret;
 }
+
+static void
+virNetDevBandwidthRateMinimal(virNetDevBandwidthRatePtr result,
+                              virNetDevBandwidthRatePtr band1,
+                              virNetDevBandwidthRatePtr band2)
+{
+    if (!band1 || !band2) {
+        memcpy(result, band1 ? band1 : band2, sizeof(*result));
+        return;
+    }
+
+    /* We can't do a simple MIN() here, because zero value doesn't mean the
+     * narrowest limit, but and unset value. Hence we need symmetric F(a, b)
+     * so that:
+     * F(a, 0) = F(0, a) = a; special corner case: F(0, 0) = 0
+     * F(a, b) = MIN(a, b) for a != 0 and b != 0
+     */
+#define NON_ZERO_MIN(a, b) \
+    ((a) && (b) ? MIN(a, b) : (a) ? (a) : (b))
+
+    result->average = NON_ZERO_MIN(band1->average, band2->average);
+    result->peak    = NON_ZERO_MIN(band1->peak,    band2->peak);
+    result->floor   = NON_ZERO_MIN(band1->floor,   band2->floor);
+    result->burst   = NON_ZERO_MIN(band1->burst,   band2->burst);
+}
+
+/**
+ * virNetDevBandwidthMinimal:
+ * @result: the minimal intersect of @band1 and @band2
+ * @band1: the first bandwidth
+ * @band2: the second bandwidth
+ *
+ * Combine the two bandwidths into one with choosing the minimal value for each
+ * pair of items within bandwidth structure. The resulting bandwidth is stored
+ * into @result. In case of both @band1 and @band2 being NULL pointers, the
+ * @ret is set to NULL as well as there's no bandwidth to calculate (this is
+ * not considered an error). The caller is responsible for freeing @result when
+ * no longer needed.
+ *
+ * Returns 0 on success, -1 otherwise.
+ */
+int
+virNetDevBandwidthMinimal(virNetDevBandwidthPtr *result,
+                          virNetDevBandwidthPtr band1,
+                          virNetDevBandwidthPtr band2)
+{
+    int ret = -1;
+
+    if (!band1 && !band2) {
+        /* Nothing to compute */
+        *result = NULL;
+        return 0;
+    }
+
+    if (!band1 || !band2) {
+        /* Sweet, one of the args is NULL. The non-NULL one
+         * is our minimum then. */
+        return virNetDevBandwidthCopy(result, band1 ? band1 : band2);
+    }
+
+    if (VIR_ALLOC(*result) < 0)
+        goto cleanup;
+
+    if (!band1->in && !band2->in) {
+        /* nada */
+    } else {
+        if (VIR_ALLOC((*result)->in) < 0)
+            goto cleanup;
+
+        virNetDevBandwidthRateMinimal((*result)->in, band1->in, band2->in);
+    }
+
+    if (!band1->out && !band2->out) {
+        /* nada */
+    } else {
+        if (VIR_ALLOC((*result)->out) < 0)
+            goto cleanup;
+
+        virNetDevBandwidthRateMinimal((*result)->out, band1->out, band2->out);
+    }
+
+    ret = 0;
+cleanup:
+    if (ret < 0)
+        VIR_FREE(*result);
+    return ret;
+}
diff --git a/src/util/virnetdevbandwidth.h b/src/util/virnetdevbandwidth.h
index 4606a07..ea40df4 100644
--- a/src/util/virnetdevbandwidth.h
+++ b/src/util/virnetdevbandwidth.h
@@ -74,4 +74,10 @@ int virNetDevBandwidthUpdateRate(const char *ifname,
                                  unsigned long long new_rate)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2)
     ATTRIBUTE_RETURN_CHECK;
+
+int
+virNetDevBandwidthMinimal(virNetDevBandwidthPtr *result,
+                          virNetDevBandwidthPtr band1,
+                          virNetDevBandwidthPtr band2)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_RETURN_CHECK;
 #endif /* __VIR_NETDEV_BANDWIDTH_H__ */
-- 
1.8.5.2


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