Re: [dpdk-dev] [PATCH] net/ixgbe: fix busy polling while fiber link update

[Ilya Maximets <i.maximets@samsung.com>]

On 04.09.2018 09:08, Zhang, Qi Z wrote:
> Hi Ilya:
> 
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ilya Maximets
>> Sent: Friday, August 31, 2018 8:40 PM
>> To: dev@dpdk.org
>> Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>; Ananyev, Konstantin
>> <konstantin.ananyev@intel.com>; Laurent Hardy
>> <laurent.hardy@6wind.com>; Dai, Wei <wei.dai@intel.com>; Ilya Maximets
>> <i.maximets@samsung.com>; stable@dpdk.org
>> Subject: [dpdk-dev] [PATCH] net/ixgbe: fix busy polling while fiber link update
>>
>> If the multispeed fiber link is in DOWN state, ixgbe_setup_link could take
>> around a second of busy polling. This is highly inconvenient for the case where
>> single thread periodically checks the link statuses. For example, OVS main
>> thread periodically updates the link statuses and hangs for a really long time
>> busy waiting on ixgbe_setup_link() for a DOWN fiber ports. For case with 3
>> down ports it hangs for a 3 seconds and unable to do anything including
>> packet processing.
>> Fix that by shifting that workaround to a separate thread by alarm handler that
>> will try to set up link if it is DOWN.
> 
> Does that mean we will block the interrupt thread for 3 seconds?

Three times for one second. Other work could be scheduled between.
IMHO, it's much better than blocking usual caller for 3 seconds.

> Also, can we guarantee there will not be any race condition if we call ixgbe_setup_link at another thread, the base code API is not assumed to be thread-safe as I know.

The only user of 'ixgbe_setup_link' is 'ixgbe_dev_start', but it could be
called only if device stopped. 'ixgbe_dev_stop' cancels the alarm.
Race with 'link_update' avoided by 'IXGBE_FLAG_NEED_LINK_CONFIG' flag.

> 
> Regards
> Qi
> 
>>
>> Fixes: c12d22f65b13 ("net/ixgbe: ensure link status is updated")
>> CC: stable@dpdk.org
>>
>> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
>> ---
>>  drivers/net/ixgbe/ixgbe_ethdev.c | 43 ++++++++++++++++++++++++--------
>>  1 file changed, 32 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c
>> b/drivers/net/ixgbe/ixgbe_ethdev.c
>> index 26b192737..a33b9a6e8 100644
>> --- a/drivers/net/ixgbe/ixgbe_ethdev.c
>> +++ b/drivers/net/ixgbe/ixgbe_ethdev.c
>> @@ -221,6 +221,8 @@ static int ixgbe_dev_interrupt_action(struct
>> rte_eth_dev *dev,
>>  				      struct rte_intr_handle *handle);  static void
>> ixgbe_dev_interrupt_handler(void *param);  static void
>> ixgbe_dev_interrupt_delayed_handler(void *param);
>> +static void ixgbe_dev_setup_link_alarm_handler(void *param);
>> +
>>  static int ixgbe_add_rar(struct rte_eth_dev *dev, struct ether_addr
>> *mac_addr,
>>  			 uint32_t index, uint32_t pool);
>>  static void ixgbe_remove_rar(struct rte_eth_dev *dev, uint32_t index); @@
>> -2791,6 +2793,8 @@ ixgbe_dev_stop(struct rte_eth_dev *dev)
>>
>>  	PMD_INIT_FUNC_TRACE();
>>
>> +	rte_eal_alarm_cancel(ixgbe_dev_setup_link_alarm_handler, dev);
>> +
>>  	/* disable interrupts */
>>  	ixgbe_disable_intr(hw);
>>
>> @@ -3969,6 +3973,25 @@ ixgbevf_check_link(struct ixgbe_hw *hw,
>> ixgbe_link_speed *speed,
>>  	return ret_val;
>>  }
>>
>> +static void
>> +ixgbe_dev_setup_link_alarm_handler(void *param) {
>> +	struct rte_eth_dev *dev = (struct rte_eth_dev *)param;
>> +	struct ixgbe_hw *hw =
>> IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
>> +	struct ixgbe_interrupt *intr =
>> +		IXGBE_DEV_PRIVATE_TO_INTR(dev->data->dev_private);
>> +	u32 speed;
>> +	bool autoneg = false;
>> +
>> +	speed = hw->phy.autoneg_advertised;
>> +	if (!speed)
>> +		ixgbe_get_link_capabilities(hw, &speed, &autoneg);
>> +
>> +	ixgbe_setup_link(hw, speed, true);
>> +
>> +	intr->flags &= ~IXGBE_FLAG_NEED_LINK_CONFIG; }
>> +
>>  /* return 0 means link status changed, -1 means not changed */  int
>> ixgbe_dev_link_update_share(struct rte_eth_dev *dev, @@ -3981,9 +4004,7
>> @@ ixgbe_dev_link_update_share(struct rte_eth_dev *dev,
>>  		IXGBE_DEV_PRIVATE_TO_INTR(dev->data->dev_private);
>>  	int link_up;
>>  	int diag;
>> -	u32 speed = 0;
>>  	int wait = 1;
>> -	bool autoneg = false;
>>
>>  	memset(&link, 0, sizeof(link));
>>  	link.link_status = ETH_LINK_DOWN;
>> @@ -3993,13 +4014,8 @@ ixgbe_dev_link_update_share(struct rte_eth_dev
>> *dev,
>>
>>  	hw->mac.get_link_status = true;
>>
>> -	if ((intr->flags & IXGBE_FLAG_NEED_LINK_CONFIG) &&
>> -		ixgbe_get_media_type(hw) == ixgbe_media_type_fiber) {
>> -		speed = hw->phy.autoneg_advertised;
>> -		if (!speed)
>> -			ixgbe_get_link_capabilities(hw, &speed, &autoneg);
>> -		ixgbe_setup_link(hw, speed, true);
>> -	}
>> +	if (intr->flags & IXGBE_FLAG_NEED_LINK_CONFIG)
>> +		return rte_eth_linkstatus_set(dev, &link);
>>
>>  	/* check if it needs to wait to complete, if lsc interrupt is enabled */
>>  	if (wait_to_complete == 0 || dev->data->dev_conf.intr_conf.lsc != 0) @@
>> -4017,11 +4033,14 @@ ixgbe_dev_link_update_share(struct rte_eth_dev *dev,
>>  	}
>>
>>  	if (link_up == 0) {
>> -		intr->flags |= IXGBE_FLAG_NEED_LINK_CONFIG;
>> +		if (ixgbe_get_media_type(hw) == ixgbe_media_type_fiber) {
>> +			intr->flags |= IXGBE_FLAG_NEED_LINK_CONFIG;
>> +			rte_eal_alarm_set(10,
>> +				ixgbe_dev_setup_link_alarm_handler, dev);
>> +		}
>>  		return rte_eth_linkstatus_set(dev, &link);
>>  	}
>>
>> -	intr->flags &= ~IXGBE_FLAG_NEED_LINK_CONFIG;
>>  	link.link_status = ETH_LINK_UP;
>>  	link.link_duplex = ETH_LINK_FULL_DUPLEX;
>>
>> @@ -5128,6 +5147,8 @@ ixgbevf_dev_stop(struct rte_eth_dev *dev)
>>
>>  	PMD_INIT_FUNC_TRACE();
>>
>> +	rte_eal_alarm_cancel(ixgbe_dev_setup_link_alarm_handler, dev);
>> +
>>  	ixgbevf_intr_disable(dev);
>>
>>  	hw->adapter_stopped = 1;
>> --
>> 2.17.1
>