Funny, everyone is trying to get more performance out of
vhost-user and you're are adding qos... :-)
I am still looking into it, so don't consider this a
throughout review.
On Fri, Oct 16, 2015 at 02:28:10PM +0100, Ian Stokes wrote:
> This patch provides the modifications required in netdev-dpdk.c and
> vswitch.xml to allow for a DPDK user space QoS algorithm.
>
> This patch adds a QoS configuration structure for netdev-dpdk and
> expected QoS operations 'dpdk_qos_ops'. Various helper functions
> are also supplied.
>
> Also included are the modifications required for vswitch.xml to allow a
> new QoS implementation for netdev-dpdk devices. This includes a new QoS type
> `egress-policer` as well as its expected QoS table entries.
>
> The QoS functionality implemented for DPDK devices is `egress-policer`.
> This can be used to drop egress packets at a configurable rate.
>
> The INSTALL.DPDK.md guide has also been modified to provide an example
> configuration of `egress-policer` QoS.
>
> Signed-off-by: Ian Stokes <ian.sto...@intel.com>
> ---
> INSTALL.DPDK.md | 20 +++
> lib/netdev-dpdk.c | 416
> +++++++++++++++++++++++++++++++++++++++++++++++++-
> vswitchd/vswitch.xml | 52 +++++++
> 3 files changed, 481 insertions(+), 7 deletions(-)
>
> diff --git a/INSTALL.DPDK.md b/INSTALL.DPDK.md
> index 7bf110c..c64b8ce 100644
> --- a/INSTALL.DPDK.md
> +++ b/INSTALL.DPDK.md
> @@ -207,6 +207,26 @@ Using the DPDK with ovs-vswitchd:
> ./ovs-ofctl add-flow br0 in_port=2,action=output:1
> ```
>
> +8. QoS usage example
> +
> + Assuming you have a vhost-user port transmitting traffic consisting of
> + packets of size 64 bytes, the following command would limit the egress
> + transmission rate of the port to ~1,000,000 packets per second:
> +
> + `ovs-vsctl set port vhost-user0 qos=@newqos -- --id=@newqos create qos
> + type=egress-policer other-config:cir=46000000 other-config:cbs=2048`
> +
> + To examine the QoS configuration of the port:
> +
> + `ovs-appctl -t ovs-vswitchd qos/show vhost-user0`
> +
> + To clear the QoS configuration from the port and ovsdb use the following:
> +
> + `ovs-vsctl -- destroy QoS vhost-user0 -- clear Port vhost-user0 qos`
> +
> + For more details regarding egress-policer parameters please refer to the
> + vswitch.xml.
> +
> Performance Tuning:
> -------------------
>
> diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
> index 93b0589..cd4c532 100644
> --- a/lib/netdev-dpdk.c
> +++ b/lib/netdev-dpdk.c
> @@ -44,6 +44,7 @@
> #include "ovs-rcu.h"
> #include "packets.h"
> #include "shash.h"
> +#include "smap.h"
> #include "sset.h"
> #include "unaligned.h"
> #include "timeval.h"
> @@ -52,12 +53,14 @@
>
> #include "rte_config.h"
> #include "rte_mbuf.h"
> +#include "rte_meter.h"
> #include "rte_virtio_net.h"
>
> VLOG_DEFINE_THIS_MODULE(dpdk);
> static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 20);
>
> #define DPDK_PORT_WATCHDOG_INTERVAL 5
> +#define DPDK_MAX_QOS_NAME_SIZE 10
>
> #define OVS_CACHE_LINE_SIZE CACHE_LINE_SIZE
> #define OVS_VPORT_DPDK "ovs_dpdk"
> @@ -142,6 +145,107 @@ static int rte_eal_init_ret = ENODEV;
>
> static struct ovs_mutex dpdk_mutex = OVS_MUTEX_INITIALIZER;
>
> +/* Quality of Service */
> +
> +/* An instance of a QoS configuration. Always associated with a particular
> + * network device.
> + *
> + * Each QoS implementation subclasses this with whatever additional data it
> + * needs.
> + */
> +struct qos_conf {
> + const struct dpdk_qos_ops *ops;
> +};
> +
> +/* A particular implementation of dpdk QoS operations.
> + *
> + * The functions below return 0 if successful or a positive errno value on
> + * failure, except where otherwise noted. All of them must be provided,
> except
> + * where otherwise noted.
> + */
> +struct dpdk_qos_ops {
> +
> + /* Name of the QoS type */
> + const char *qos_name;
> +
> + /* Called to construct the QoS implementation on 'netdev'. The
> + * implementation should make the appropriate calls to configure QoS
> + * according to 'details'. The implementation may assume that any current
> + * QoS configuration already installed should be destroyed before
> + * constructing the new configuration.
> + *
> + * The contents of 'details' should be documented as valid for 'ovs_name'
> + * in the "other_config" column in the "QoS" table in
> vswitchd/vswitch.xml
> + * (which is built as ovs-vswitchd.conf.db(8)).
> + *
> + * This function must return 0 if and only if it sets 'netdev->qos_conf'
> + * to an initialized 'struct qos_conf'.
> + *
> + * For all QoS implementations it should always be non-null.
> + */
> + int (*qos_construct)(struct netdev *netdev, const struct smap *details);
> +
> + /* Destroys the data structures allocated by the implementation as part
> of
> + * 'qos_conf.
> + *
> + * For all QoS implementations it should always be non-null.
> + */
> + void (*qos_destruct)(struct netdev *netdev, struct qos_conf *conf);
> +
> + /* Retrieves details of 'netdev->qos_conf' configuration into 'details'.
> + *
> + * The contents of 'details' should be documented as valid for 'ovs_name'
> + * in the "other_config" column in the "QoS" table in
> vswitchd/vswitch.xml
> + * (which is built as ovs-vswitchd.conf.db(8)).
> + */
> + int (*qos_get)(const struct netdev *netdev, struct smap *details);
> +
> + /* Reconfigures 'netdev->qos_conf' according to 'details', performing any
> + * required calls to complete the reconfiguration.
> + *
> + * The contents of 'details' should be documented as valid for 'ovs_name'
> + * in the "other_config" column in the "QoS" table in
> vswitchd/vswitch.xml
> + * (which is built as ovs-vswitchd.conf.db(8)).
> + *
> + * This function may be null if 'qos_conf' is not configurable.
> + */
> + int (*qos_set)(struct netdev *netdev, const struct smap *details);
> +
> + /* Modify an array of rte_mbufs. The modification is specific to
> + * each qos implementation.
> + *
> + * The function should take and array of mbufs and an int representing
> + * the current number of mbufs present in the array.
> + *
> + * After the function has performed a qos modification to the array of
> + * mbufs it returns an int representing the number of mbufs now present
> in
> + * the array. This value is can then be passed to the port send function
> + * along with the modified array for transmission.
> + *
> + * For all QoS implementations it should always be non-null.
> + */
> + int (*qos_alg_process)(struct netdev *netdev, struct rte_mbuf **pkts,
> + int pkt_cnt);
> +};
> +
> +/* dpdk_qos_ops for each type of user space QoS implementation */
> +static const struct dpdk_qos_ops egress_policer_ops;
> +
> +/*
> + * Array of dpdk_qos_ops, contains pointer to all supported QoS
> + * operations.
> + */
> +static const struct dpdk_qos_ops *const qos_confs[] = {
> + &egress_policer_ops,
> + NULL
> +};
> +
> +/* Action that can be set for a packet for rte_meter */
> +enum egress_policer_action {
> + GREEN = e_RTE_METER_GREEN,
> + DROP = 1,
> +};
> +
> /* Contains all 'struct dpdk_dev's. */
> static struct ovs_list dpdk_list OVS_GUARDED_BY(dpdk_mutex)
> = OVS_LIST_INITIALIZER(&dpdk_list);
> @@ -235,6 +339,11 @@ struct netdev_dpdk {
>
> /* In dpdk_list. */
> struct ovs_list list_node OVS_GUARDED_BY(dpdk_mutex);
> +
> + /* QoS configuration and lock for the device */
> + struct qos_conf *qos_conf;
> + rte_spinlock_t qos_lock;
> +
> };
>
> struct netdev_rxq_dpdk {
> @@ -614,6 +723,10 @@ netdev_dpdk_init(struct netdev *netdev_, unsigned int
> port_no,
> goto unlock;
> }
>
> + /* Initialise QoS configuration to NULL and qos lock to unlocked */
> + netdev->qos_conf = NULL;
> + rte_spinlock_init(&netdev->qos_lock);
> +
> netdev_->n_txq = NR_QUEUE;
> netdev_->n_rxq = NR_QUEUE;
> netdev->real_n_txq = NR_QUEUE;
> @@ -1038,6 +1151,21 @@ netdev_dpdk_rxq_recv(struct netdev_rxq *rxq_, struct
> dp_packet **packets,
> return 0;
> }
>
> +static inline int
> +netdev_dpdk_qos_process__(struct netdev_dpdk *dev, struct rte_mbuf **pkts,
> + int cnt)
> +{
> + struct netdev *netdev = &dev->up;
> +
People are working really hard to get the data path as fast
as possible and this seems to be too expensive:
> + rte_spinlock_lock(&dev->qos_lock);
> + if (dev->qos_conf != NULL) {
> + cnt = dev->qos_conf->ops->qos_alg_process(netdev, pkts, cnt);
> + }
> + rte_spinlock_unlock(&dev->qos_lock);
Maybe we could do something like this:
if (dev->qos_conf != NULL) {
rte_spinlock_lock(&dev->qos_lock);
if (dev->qos_conf != NULL) {
cnt = dev->qos_conf->ops->qos_alg_process(netdev, pkts, cnt);
}
rte_spinlock_unlock(&dev->qos_lock);
}
Though I still have to look at qos_alg_process() to see if the locking
could be done in another way.
> +
> + return cnt;
> +}
> +
> static inline void
> netdev_dpdk_vhost_update_tx_counters(struct netdev_stats *stats,
> struct dp_packet **packets,
> @@ -1072,6 +1200,9 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, struct
> dp_packet **pkts,
> goto out;
> }
>
> + /* Check has QoS has been configured for the netdev */
> + cnt = netdev_dpdk_qos_process__(vhost_dev, cur_pkts, cnt);
> +
> /* There is vHost TX single queue, So we need to lock it for TX. */
> rte_spinlock_lock(&vhost_dev->vhost_tx_lock);
>
> @@ -1216,6 +1347,10 @@ dpdk_do_tx_copy(struct netdev *netdev, int qid, struct
> dp_packet **pkts,
> if (dev->type == DPDK_DEV_VHOST) {
> __netdev_dpdk_vhost_send(netdev, (struct dp_packet **) mbufs,
> newcnt, true);
> } else {
> +
> + /* Check if QoS has been configured for this netdev. */
> + newcnt = netdev_dpdk_qos_process__(dev, mbufs, newcnt);
> +
> dpdk_queue_pkts(dev, qid, mbufs, newcnt);
> dpdk_queue_flush(dev, qid);
> }
> @@ -1275,9 +1410,15 @@ netdev_dpdk_send__(struct netdev_dpdk *dev, int qid,
>
> if (OVS_UNLIKELY(size > dev->max_packet_len)) {
> if (next_tx_idx != i) {
> + cnt = i - next_tx_idx;
> +
> + cnt = netdev_dpdk_qos_process__(dev,
> + (struct rte_mbuf**)pkts,
> + cnt);
I have another concern at this point because for each batch it
will grab a lock pretty much serializing multiple queues.
> +
> dpdk_queue_pkts(dev, qid,
> (struct rte_mbuf **)&pkts[next_tx_idx],
> - i-next_tx_idx);
> + cnt);
> }
>
> VLOG_WARN_RL(&rl, "Too big size %d max_packet_len %d",
> @@ -1289,9 +1430,12 @@ netdev_dpdk_send__(struct netdev_dpdk *dev, int qid,
> }
> }
> if (next_tx_idx != cnt) {
> - dpdk_queue_pkts(dev, qid,
> - (struct rte_mbuf **)&pkts[next_tx_idx],
> - cnt-next_tx_idx);
> + cnt -= next_tx_idx;
> +
> + cnt = netdev_dpdk_qos_process__(dev, (struct rte_mbuf**)pkts,
> cnt);
Same here.
and it seems it should update tx_dropped too.
Thanks,
fbl
> +
> + dpdk_queue_pkts(dev, qid, (struct rte_mbuf **)&pkts[next_tx_idx],
> + cnt);
> }
>
> if (OVS_UNLIKELY(dropped)) {
> @@ -2032,6 +2176,264 @@ unlock_dpdk:
> return err;
> }
>
> +/* QoS Functions */
> +
> +/*
> + * Initialize QoS configuration operations.
> + */
> +static void
> +qos_conf_init(struct qos_conf *conf, const struct dpdk_qos_ops *ops)
> +{
> + conf->ops = ops;
> +}
> +
> +/*
> + * Search existing QoS operations in qos_ops and compare each set of
> + * operations qos_name to name. Return a dpdk_qos_ops pointer to a match,
> + * else return NULL
> + */
> +static const struct dpdk_qos_ops *
> +qos_lookup_name(const char *name)
> +{
> + const struct dpdk_qos_ops *const *opsp;
> +
> + for (opsp = qos_confs; *opsp != NULL; opsp++) {
> + const struct dpdk_qos_ops *ops = *opsp;
> + if (!strncmp(name, ops->qos_name,DPDK_MAX_QOS_NAME_SIZE)) {
> + return ops;
> + }
> + }
> + return NULL;
> +}
> +
> +/*
> + * Call qos_destruct to clean up items associated with the netdevs
> + * qos_conf. Set netdevs qos_conf to NULL.
> + */
> +static void
> +qos_delete_conf(struct netdev *netdev_)
> +{
> + struct netdev_dpdk *netdev = netdev_dpdk_cast(netdev_);
> +
> + rte_spinlock_lock(&netdev->qos_lock);
> + if (netdev->qos_conf) {
> + if (netdev->qos_conf->ops->qos_destruct) {
> + netdev->qos_conf->ops->qos_destruct(netdev_, netdev->qos_conf);
> + }
> + netdev->qos_conf = NULL;
> + }
> + rte_spinlock_unlock(&netdev->qos_lock);
> +}
> +
> +static int
> +netdev_dpdk_get_qos_types(const struct netdev *netdev OVS_UNUSED,
> + struct sset *types)
> +{
> + const struct dpdk_qos_ops *const *opsp;
> +
> + for (opsp = qos_confs; *opsp != NULL; opsp++) {
> + const struct dpdk_qos_ops *ops = *opsp;
> + if (ops->qos_construct && ops->qos_name[0] != '\0') {
> + sset_add(types, ops->qos_name);
> + }
> + }
> + return 0;
> +}
> +
> +static int
> +netdev_dpdk_get_qos(const struct netdev *netdev_,
> + const char **typep, struct smap *details)
> +{
> + struct netdev_dpdk *netdev = netdev_dpdk_cast(netdev_);
> + int error = 0;
> +
> + ovs_mutex_lock(&netdev->mutex);
> + if(netdev->qos_conf) {
> + *typep = netdev->qos_conf->ops->qos_name;
> + error = (netdev->qos_conf->ops->qos_get
> + ? netdev->qos_conf->ops->qos_get(netdev_, details): 0);
> + }
> + ovs_mutex_unlock(&netdev->mutex);
> +
> + return error;
> +}
> +
> +static int
> +netdev_dpdk_set_qos(struct netdev *netdev_,
> + const char *type, const struct smap *details)
> +{
> + struct netdev_dpdk *netdev = netdev_dpdk_cast(netdev_);
> + const struct dpdk_qos_ops *new_ops = NULL;
> + int error = 0;
> +
> + /* If type is empty the current QoS configuration for the dpdk-netdev can
> + * be destroyed */
> + if(type[0] == '\0') {
> + qos_delete_conf(netdev_);
> + }
> +
> + new_ops = qos_lookup_name(type);
> + if (!new_ops || !new_ops->qos_construct) {
> + return EOPNOTSUPP;
> + }
> +
> + ovs_mutex_lock(&netdev->mutex);
> + if (netdev->qos_conf) {
> + if (new_ops == netdev->qos_conf->ops) {
> + error = new_ops->qos_set ? new_ops->qos_set(netdev_, details) :
> 0;
> + }
> + else {
> + /* Delete existing QoS configuration. */
> + qos_delete_conf(netdev_);
> + ovs_assert(netdev->qos_conf == NULL);
> +
> + /* Install new QoS configuration. */
> + error = new_ops->qos_construct(netdev_, details);
> + ovs_assert((error == 0) == (netdev->qos_conf != NULL));
> + }
> + } else {
> + error = new_ops->qos_construct(netdev_, details);
> + ovs_assert((error == 0) == (netdev->qos_conf != NULL));
> + }
> +
> + ovs_mutex_unlock(&netdev->mutex);
> + return error;
> +}
> +
> +/* egress-policer details */
> +
> +struct egress_policer {
> + struct qos_conf qos_conf;
> + struct rte_meter_srtcm_params app_srtcm_params;
> + struct rte_meter_srtcm test_meter;
> +};
> +
> +static struct egress_policer *
> +egress_policer_get__(const struct netdev *netdev_)
> +{
> + struct netdev_dpdk *netdev = netdev_dpdk_cast(netdev_);
> + return CONTAINER_OF(netdev->qos_conf, struct egress_policer, qos_conf);
> +}
> +
> +static int
> +egress_policer_qos_construct(struct netdev *netdev_,
> + const struct smap *details)
> +{
> + struct netdev_dpdk *netdev = netdev_dpdk_cast(netdev_);
> + struct egress_policer *policer;
> + const char *cir_s;
> + const char *cbs_s;
> + int err = 0;
> +
> + rte_spinlock_lock(&netdev->qos_lock);
> + policer = xmalloc(sizeof *policer);
> + qos_conf_init(&policer->qos_conf, &egress_policer_ops);
> + netdev->qos_conf = &policer->qos_conf;
> + cir_s = smap_get(details, "cir");
> + cbs_s = smap_get(details, "cbs");
> + policer->app_srtcm_params.cir = cir_s ? strtoull(cir_s, NULL, 10) : 0;
> + policer->app_srtcm_params.cbs = cbs_s ? strtoull(cbs_s, NULL, 10) : 0;
> + policer->app_srtcm_params.ebs = 0;
> + err = rte_meter_srtcm_config(&policer->test_meter,
> + &policer->app_srtcm_params);
> + rte_spinlock_unlock(&netdev->qos_lock);
> +
> + return err;
> +}
> +
> +static void
> +egress_policer_qos_destruct(struct netdev *netdev_ OVS_UNUSED,
> + struct qos_conf *conf)
> +{
> + struct egress_policer *policer = CONTAINER_OF(conf, struct
> egress_policer,
> + qos_conf);
> + free(policer);
> +}
> +
> +static int
> +egress_policer_qos_get(const struct netdev *netdev, struct smap *details)
> +{
> + struct egress_policer *policer = egress_policer_get__(netdev);
> + smap_add_format(details, "cir", "%llu",
> + 1ULL * policer->app_srtcm_params.cir);
> + smap_add_format(details, "cbs", "%llu",
> + 1ULL * policer->app_srtcm_params.cbs);
> + return 0;
> +}
> +
> +static int
> +egress_policer_qos_set(struct netdev *netdev_, const struct smap *details)
> +{
> + struct egress_policer *policer;
> + const char *cir_s;
> + const char *cbs_s;
> + int err = 0;
> +
> + policer = egress_policer_get__(netdev_);
> + cir_s = smap_get(details, "cir");
> + cbs_s = smap_get(details, "cbs");
> + policer->app_srtcm_params.cir = cir_s ? strtoull(cir_s, NULL, 10) : 0;
> + policer->app_srtcm_params.cbs = cbs_s ? strtoull(cbs_s, NULL, 10) : 0;
> + policer->app_srtcm_params.ebs = 0;
> + err = rte_meter_srtcm_config(&policer->test_meter,
> + &policer->app_srtcm_params);
> +
> + return err;
> +}
> +
> +static inline int
> +egress_policer_pkt_handle__(struct rte_meter_srtcm *meter,
> + struct rte_mbuf *pkt, uint64_t time)
> +{
> + uint8_t output_color;
> + uint32_t pkt_len = rte_pktmbuf_pkt_len(pkt) - sizeof(struct ether_hdr);
> + enum egress_policer_action action = GREEN;
> +
> + /* color input is not used for blind modes */
> + output_color = (uint8_t) rte_meter_srtcm_color_blind_check(meter, time,
> + pkt_len);
> +
> + /* Check output color, 0 corresponds to GREEN i.e. packet can be
> + * transmitted. If greater than 0 then action is set to DROP. */
> + if (output_color) {
> + action = DROP;
> + }
> +
> + return action;
> +}
> +
> +static int
> +egress_policer_alg_process(struct netdev *netdev_, struct rte_mbuf **pkts,
> + int pkt_cnt)
> +{
> + int i = 0;
> + int cnt = pkt_cnt;
> + struct egress_policer *policer = egress_policer_get__(netdev_);
> + struct rte_mbuf *pkt = NULL;
> + uint64_t current_time = rte_rdtsc();
> +
> + for(i = 0; i < pkt_cnt; i++) {
> + pkt = pkts[i];
> + /* Handle current packet */
> + if (egress_policer_pkt_handle__(&policer->test_meter, pkt,
> + current_time) == DROP) {
> + rte_pktmbuf_free(pkt);
> + cnt = cnt - 1;
> + }
> + }
> +
> + return cnt;
> +}
> +
> +static const struct dpdk_qos_ops egress_policer_ops = {
> + "egress-policer", /* qos_name */
> + egress_policer_qos_construct,
> + egress_policer_qos_destruct,
> + egress_policer_qos_get,
> + egress_policer_qos_set,
> + egress_policer_alg_process
> +};
> +
> #define NETDEV_DPDK_CLASS(NAME, INIT, CONSTRUCT, DESTRUCT, MULTIQ, SEND, \
> GET_CARRIER, GET_STATS, GET_FEATURES, GET_STATUS, RXQ_RECV) \
> { \
> @@ -2069,10 +2471,10 @@ unlock_dpdk:
> NULL, /* set_advertisements */ \
> \
> NULL, /* set_policing */ \
> - NULL, /* get_qos_types */ \
> + netdev_dpdk_get_qos_types, \
> NULL, /* get_qos_capabilities */ \
> - NULL, /* get_qos */ \
> - NULL, /* set_qos */ \
> + netdev_dpdk_get_qos, \
> + netdev_dpdk_set_qos, \
> NULL, /* get_queue */ \
> NULL, /* set_queue */ \
> NULL, /* delete_queue */ \
> diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
> index 4dbd9e3..5be8eb6 100644
> --- a/vswitchd/vswitch.xml
> +++ b/vswitchd/vswitch.xml
> @@ -3298,6 +3298,26 @@
> for information on how this classifier works.
> </dd>
> </dl>
> + <dl>
> + <dt><code>egress-policer</code></dt>
> + <dd>
> + An egress policer algorithm. This implementation uses the DPDK
> + rte_meter library. The rte_meter library provides an implementation
> + of srTCM (RFC2697) which allows the metering and policing of
> traffic.
> + The implementation in OVS creates a color blind srTCM meter with a
> + single token bucket used to police traffic. It should be noted that
> + when the rte_meter is configured as part of QoS there will be a
> + performance overhead as the rte_mter itself will consume CPU cycles
> + in order to police traffic. These CPU cycles ordinarily are used
> for
> + packet proccessing. As such the drop in performance will be noticed
> + in terms of overall aggregate traffic throughput.
> +
> + For more information regarding the usage of the DPDK rte_meter see
> +
> <code>http://dpdk.org/doc/guides/sample_app_ug/qos_metering.html</code>
> + For more information regarding srTCM see
> + <code>https://tools.ietf.org/html/rfc2697</code>
> + </dd>
> + </dl>
> </column>
>
> <column name="queues">
> @@ -3334,6 +3354,38 @@
> </column>
> </group>
>
> + <group title="Configuration for egress-policer QoS">
> + <p>
> + <ref table="QoS"/> <ref table="QoS" column="type"/>
> + <code>egress-policer</code> provides egress policing for userspace
> + port types with DPDK.
> +
> + It has the following key-value pairs defined.
> + </p>
> +
> + <column name="other_config" key="cir" type='{"type": "integer"}'>
> + The Committed Information Rate (CIR) is measured in bytes of IP
> + packets per second, i.e. it includes the IP header, but not link
> + specific (e.g. Ethernet) headers. This represents the bytes per
> second
> + rate at which the token bucket will be updated. The cir value is
> + calculated by (pps x packet data size). For example assuming a user
> + wishes to limit a stream consisting of 64 byte packets to 1 million
> + packets per second the CIR would be set to to to 46000000. This value
> + can be broken into '1,000,000 x 46'. Where 1,000,000 is the policing
> + rate for the number of packets per second and 46 represents the size
> + of the packet data for a 64 byte ip packet.
> + </column>
> + <column name="other_config" key="cbs" type='{"type": "integer"}'>
> + The Committed Burst Size (CBS) is measured in bytes and represents a
> + token bucket. At a minimum this value should be be set to the
> expected
> + largest size packet in the traffic stream. In practice larger values
> + may be used to increase the size of the token bucket. If a packet can
> + be transmitted then the cbs will be decremented by the number of
> + bytes/tokens of the packet. If there are not enough tokens in the cbs
> + bucket the packet will be dropped.
> + </column>
> + </group>
> +
> <group title="Common Columns">
> The overall purpose of these columns is described under <code>Common
> Columns</code> at the beginning of this document.
> --
> 1.7.4.1
>
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