[ovs-dev] [PATCH v4 3/3] netdev-dpdk: Enable vhost-tx-retries config.

Ian Stokes ian.stokes at intel.com
Thu Jul 4 13:59:16 UTC 2019


On 7/4/2019 12:15 PM, Ilya Maximets wrote:
> Few comments inline.
> Probably, could be fixed while applying the patch.

Ok, these look reasonable to me. I can apply them this evening before 
committing.

If I add these will I had an ACK for you Ilya?

Regards
Ian
> 
> On 02.07.2019 3:32, Kevin Traynor wrote:
>> vhost tx retries can provide some mitigation against
>> dropped packets due to a temporarily slow guest/limited queue
>> size for an interface, but on the other hand when a system
>> is fully loaded those extra cycles retrying could mean
>> packets are dropped elsewhere.
>>
>> Up to now max vhost tx retries have been hardcoded, which meant
>> no tuning and no way to disable for debugging to see if extra
>> cycles spent retrying resulted in rx drops on some other
>> interface.
>>
>> Add an option to change the max retries, with a value of
>> 0 effectively disabling vhost tx retries.
>>
>> Signed-off-by: Kevin Traynor <ktraynor at redhat.com>
>> Acked-by: Eelco Chaudron <echaudro at redhat.com>
>> Acked-by: Flavio Leitner <fbl at sysclose.org>
>> ---
>>   Documentation/topics/dpdk/vhost-user.rst | 28 +++++++++++++++++
>>   lib/netdev-dpdk.c                        | 39 +++++++++++++++++++++---
>>   vswitchd/vswitch.xml                     | 12 ++++++++
>>   3 files changed, 75 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst
>> index 368f44520..724aa62f6 100644
>> --- a/Documentation/topics/dpdk/vhost-user.rst
>> +++ b/Documentation/topics/dpdk/vhost-user.rst
>> @@ -351,4 +351,29 @@ The default value is ``false``.
>>   .. _dpdk-testpmd:
>>   
>> +vhost-user-client tx retries config
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +For vhost-user-client interfaces, the max amount of retries can be changed from
>> +the default 8 by setting ``tx-retries-max``.
>> +
>> +The minimum is 0 which means there will be no retries and if any packets in
>> +each batch cannot be sent immediately they will be dropped. The maximum is 32,
>> +which would mean that after the first packet(s) in the batch was sent there
>> +could be a maximum of 32 more retries.
>> +
>> +Retries can help with avoiding packet loss when temporarily unable to send to a
>> +vhost interface because the virtqueue is full. However, spending more time
>> +retrying to send to one interface, will reduce the time available for rx/tx and
>> +processing packets on other interfaces, so some tuning may be required for best
>> +performance.
>> +
>> +Tx retries max can be set for vhost-user-client ports::
>> +
>> +    $ ovs-vsctl set Interface vhost-client-1 options:tx-retries-max=0
>> +
>> +.. note::
>> +
>> +  Configurable vhost tx retries are not supported with vhost-user ports.
>> +
>>   DPDK in the Guest
>>   -----------------
>> @@ -496,4 +521,7 @@ packets can be sent, it may mean the guest is not accepting packets, so there
>>   are no (more) retries.
>>   
>> +For information about configuring the maximum amount of tx retries for
>> +vhost-user-client interfaces see `vhost-user-client tx retries config`_.
>> +
>>   .. note::
>>   
>> diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
>> index d3e02d389..b8592962f 100644
>> --- a/lib/netdev-dpdk.c
>> +++ b/lib/netdev-dpdk.c
>> @@ -165,5 +165,10 @@ typedef uint16_t dpdk_port_t;
>>   #define DPDK_PORT_ID_FMT "%"PRIu16
>>   
>> -#define VHOST_ENQ_RETRY_NUM 8
>> +/* Minimum amount of vhost tx retries, effectively a disable. */
>> +#define VHOST_ENQ_RETRY_MIN 0
>> +/* Maximum amount of vhost tx retries. */
>> +#define VHOST_ENQ_RETRY_MAX 32
>> +/* Legacy default value for vhost tx retries. */
>> +#define VHOST_ENQ_RETRY_DEF 8
> 
> An empty line would be nice here.
> 
>>   #define IF_NAME_SZ (PATH_MAX > IFNAMSIZ ? PATH_MAX : IFNAMSIZ)
>>   
>> @@ -418,5 +423,7 @@ struct netdev_dpdk {
>>           /* True if vHost device is 'up' and has been reconfigured at least once */
>>           bool vhost_reconfigured;
>> -        /* 3 pad bytes here. */
>> +
>> +        atomic_uint8_t vhost_tx_retries_max;
>> +        /* 2 pad bytes here. */
>>       );
>>   
>> @@ -1262,4 +1269,6 @@ vhost_common_construct(struct netdev *netdev)
>>       }
>>   
>> +    atomic_store_relaxed(&dev->vhost_tx_retries_max, VHOST_ENQ_RETRY_DEF);
> 
> This should be atomic_init().
> 
>> +
>>       return common_construct(netdev, DPDK_ETH_PORT_ID_INVALID,
>>                               DPDK_DEV_VHOST, socket_id);
>> @@ -1922,4 +1931,5 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev,
>>       struct netdev_dpdk *dev = netdev_dpdk_cast(netdev);
>>       const char *path;
>> +    int max_tx_retries, cur_max_tx_retries;
>>   
>>       ovs_mutex_lock(&dev->mutex);
>> @@ -1938,4 +1948,17 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev,
>>           }
>>       }
>> +
>> +    max_tx_retries = smap_get_int(args, "tx-retries-max",
>> +                                  VHOST_ENQ_RETRY_DEF);
>> +    if (max_tx_retries < VHOST_ENQ_RETRY_MIN
>> +        || max_tx_retries > VHOST_ENQ_RETRY_MAX) {
>> +        max_tx_retries = VHOST_ENQ_RETRY_DEF;
>> +    }
>> +    atomic_read_relaxed(&dev->vhost_tx_retries_max, &cur_max_tx_retries);
>> +    if (max_tx_retries != cur_max_tx_retries) {
>> +        atomic_store_relaxed(&dev->vhost_tx_retries_max, max_tx_retries);
>> +        VLOG_INFO("Max Tx retries for vhost device '%s' set to %d",
>> +                  dev->up.name, max_tx_retries);
> 
> s/dev->up.name/netdev_get_name(netdev)/
> 
>> +    }
>>       ovs_mutex_unlock(&dev->mutex);
>>   
>> @@ -2351,4 +2374,5 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
>>       unsigned int dropped = 0;
>>       int i, retries = 0;
>> +    int max_retries = VHOST_ENQ_RETRY_MIN;
>>       int vid = netdev_dpdk_get_vid(dev);
>>   
>> @@ -2380,9 +2404,16 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
>>               /* Prepare for possible retry.*/
>>               cur_pkts = &cur_pkts[tx_pkts];
>> +            if (OVS_UNLIKELY(cnt && !retries)) {
>> +                /*
>> +                 * Read max retries as there are packets not sent
>> +                 * and no retries have already occurred.
>> +                 */
>> +                atomic_read_relaxed(&dev->vhost_tx_retries_max, &max_retries);
>> +            }
>>           } else {
>>               /* No packets sent - do not retry.*/
>>               break;
>>           }
>> -    } while (cnt && (retries++ < VHOST_ENQ_RETRY_NUM));
>> +    } while (cnt && (retries++ < max_retries));
>>   
>>       rte_spinlock_unlock(&dev->tx_q[qid].tx_lock);
>> @@ -2391,5 +2422,5 @@ __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
>>       netdev_dpdk_vhost_update_tx_counters(&dev->stats, pkts, total_pkts,
>>                                            cnt + dropped);
>> -    dev->tx_retries += MIN(retries, VHOST_ENQ_RETRY_NUM);
>> +    dev->tx_retries += MIN(retries, max_retries);
>>       rte_spinlock_unlock(&dev->stats_lock);
>>   
>> diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
>> index 69fce7ffb..5b4c13b64 100644
>> --- a/vswitchd/vswitch.xml
>> +++ b/vswitchd/vswitch.xml
>> @@ -3120,4 +3120,16 @@ ovs-vsctl add-port br0 p0 -- set Interface p0 type=patch options:peer=p1 \
>>         </column>
>>   
>> +      <column name="options" key="tx-retries-max"
>> +              type='{"type": "integer", "minInteger": 0, "maxInteger": 32}'>
>> +        <p>
>> +          The value specifies the maximum amount of vhost tx retries that can
>> +          be made while trying to send a batch of packets to an interface.
>> +          Only supported by dpdkvhostuserclient interfaces.
>> +        </p>
>> +        <p>
>> +          Default value is 8.
>> +        </p>
>> +      </column>
>> +
>>         <column name="options" key="n_rxq_desc"
>>                 type='{"type": "integer", "minInteger": 1, "maxInteger": 4096}'>
>>



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