Subject: Re: [PATCH v5 net-next 11/27] bonding: rework bond_3ad_xmit_xor() to use bond_for_each_slave() only

From: Veaceslav Falico <[email-masked]>
Date: Thu, 26 Sep 2013 07:43:17 +0200

On Thu, Sep 26, 2013 at 10:31:35AM +0800, Ding Tianhong wrote:

First of all - thanks a lot for the review! Answered below.

>On 2013/9/25 15:20, Veaceslav Falico wrote:
>> Currently, there are two loops - first we find the first slave in an
>> aggregator after the xmit_hash_policy() returned number, and after that we
>> loop from that slave, over bonding head, and till that slave to find any
>> suitable slave to send the packet through.
>>
>> Replace it by just one bond_for_each_slave() loop, which first loops
>> through the requested number of slaves, saving the first suitable one, and
>> after that we've hit the requested number of slaves to skip - search for
>> any up slave to send the packet through. If we don't find such kind of
>> slave - then just send the packet through the first suitable slave found.
>>
>> Logic remains unchainged, and we skip two loops. Also, refactor it a bit
>> for readability.
>>
>> CC: Jay Vosburgh <[email-masked]>
>> CC: Andy Gospodarek <[email-masked]>
>> Signed-off-by: Veaceslav Falico <[email-masked]>
>> ---
>>
>> Notes:
>>     v4  -> v5
>>     No change.
>>
>>     v3  -> v4:
>>     No change.
>>
>>     v2  -> v3:
>>     No change.
>>
>>     v1  -> v2:
>>     No changes.
>>
>>     RFC -> v1:
>>     New patch.
>>
>>  drivers/net/bonding/bond_3ad.c | 46 ++++++++++++++++++++----------------------
>>  1 file changed, 22 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>> index 3847aee..c861ee7 100644
>> --- a/drivers/net/bonding/bond_3ad.c
>> +++ b/drivers/net/bonding/bond_3ad.c
>> @@ -2417,15 +2417,15 @@ int bond_3ad_get_active_agg_info(struct bonding *bond, struct ad_info *ad_info)
>>
>>  int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>>  {
>> -	struct slave *slave, *start_at;
>>  	struct bonding *bond = netdev_priv(dev);
>> +	struct slave *slave, *first_ok_slave;
>> +	struct aggregator *agg;
>> +	struct ad_info ad_info;
>>  	struct list_head *iter;
>> -	int slave_agg_no;
>>  	int slaves_in_agg;
>> -	int agg_id;
>> -	int i;
>> -	struct ad_info ad_info;
>> +	int slave_agg_no;
>>  	int res = 1;
>> +	int agg_id;
>>
>>  	read_lock(&bond->lock);
>>  	if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
>> @@ -2438,20 +2438,28 @@ int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>>  	agg_id = ad_info.aggregator_id;
>>
>>  	if (slaves_in_agg == 0) {
>> -		/*the aggregator is empty*/
>>  		pr_debug("%s: Error: active aggregator is empty\n", dev->name);
>>  		goto out;
>>  	}
>>
>>  	slave_agg_no = bond->xmit_hash_policy(skb, slaves_in_agg);
>> +	first_ok_slave = NULL;
>>
>>  	bond_for_each_slave(bond, slave, iter) {
>> -		struct aggregator *agg = SLAVE_AD_INFO(slave).port.aggregator;
>> +		agg = SLAVE_AD_INFO(slave).port.aggregator;
>> +		if (!agg || agg->aggregator_identifier != agg_id)
>> +			continue;
>>
>> -		if (agg && (agg->aggregator_identifier == agg_id)) {
>> +		if (slave_agg_no >= 0) {
>> +			if (!first_ok_slave && SLAVE_IS_OK(slave))
>> +				first_ok_slave = slave;
>>  			slave_agg_no--;
>> -			if (slave_agg_no < 0)
>> -				break;
>> +			continue;
>> +		}

[1]		^^^^^^^^^^^^^^^^^^^^^^^^^

>> +
>> +		if (SLAVE_IS_OK(slave)) {
>> +			res = bond_dev_queue_xmit(bond, skb, slave->dev);
>> +			goto out;
>>  		}

[2]		^^^^^^^^^^^^^^^^^^^^^^^^^

>
>I think you miss something, you will send skb always by the first suitable port,
>it could not support load balance.

Well, yes, it will send always by the first suitable port AFTER
slave_agg_no, returned by the xmit_hash_policy(), which is the whole point
in the hash function and in the load balance.

It will first loop through the slaves, decrementing slave_agg_no to a
negative value, while saving the first good to send slave, as shown in [1].
Notice the "continue;":

if (slave_agg_no >= 0) {
	if (!first_ok_slave && SLAVE_IS_OK(slave))
		first_ok_slave = slave;
	slave_agg_no--;
	continue;
}

Once we hit the negative value - which means we've skipped enough slaves,
as requested by the hash function - we can start looking for the first
slave that is good to send AFTER those all skipped slaves, as shown in [2].

Down the patch we also use that 'first_ok_slave' - in case we didn't find
any suitable one after we've skipped first slave_agg_no and till the last
slave, so it implements the same 'circular' logic as was in
bond_for_each_slave_from().

>pls consult my function.
> 		if (agg && (agg->aggregator_identifier == agg_id)) {
>-			slave_agg_no--;
>-			if (slave_agg_no < 0)
>-				break;
>+			if (--slave_agg_no < 0) {
>+				if (SLAVE_IS_OK(slave)) {
>+					res = bond_dev_queue_xmit(bond,
>+						skb, slave->dev);
>+					goto out;
>+				}
>+			}

I'll review your function in your patch.

> 		}
> 	}
>
>>  	}
>>
>> @@ -2461,20 +2469,10 @@ int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>>  		goto out;
>>  	}
>>
>> -	start_at = slave;
>> -
>> -	bond_for_each_slave_from(bond, slave, i, start_at) {
>> -		int slave_agg_id = 0;
>> -		struct aggregator *agg = SLAVE_AD_INFO(slave).port.aggregator;
>> -
>> -		if (agg)
>> -			slave_agg_id = agg->aggregator_identifier;
>> -
>> -		if (SLAVE_IS_OK(slave) && agg && (slave_agg_id == agg_id)) {
>> -			res = bond_dev_queue_xmit(bond, skb, slave->dev);
>> -			break;
>> -		}
>> -	}
>> +	/* we couldn't find any suitable slave after the agg_no, so use the
>> +	 * first suitable found, if found. */
>> +	if (first_ok_slave)
>> +		res = bond_dev_queue_xmit(bond, skb, first_ok_slave->dev);
>>
>>  out:
>>  	read_unlock(&bond->lock);
>>
>
>