Subject: Re: [PATCH] bonding-tlb: better balance when choosing slaves

From: Jay Vosburgh <[email-masked]>
Date: Tue, 05 Apr 2011 21:46:12 -0700

Weiping Pan <[email-masked]> wrote:

>On 04/03/2011 02:25 AM, Jay Vosburgh wrote:
>>> tlb_get_least_loaded_slave() always chooses slave from
>>> bonding->first_slave, that gives the beginnig slaves more chances to be used.
>>>
>>> Let tlb_get_least_loaded_slave() chooses slave from a random positon in the
>>> slave list, make all slaves transmit packets more balanced.
>> 	If outgoing traffic is not being starved (i.e., connections are
>> being balanced such that they are stacking up on one slave but
>> under-utilizing another), then I don't understand what benefit this has.
>>
>> 	There is already some degree of randomness, as peers will be
>> assigned in the order that packets are transmitted to them after each
>> rebalance.  The busiest peers will tend to be on the earlier slaves, and
>> vice versa, but I'm not sure this is a bad thing.
>>
>> 	Does this have any real gain other than making the rx/tx
>> statistics for the slaves more equal over time?
>>
>> 	I haven't measured it, but I would expect that for small numbers
>> of peers, having them tend to stay on the same slaves over time is
>> probably a good thing.
>modprobe bonding mode=balance-tlb miimon=100
>ifconfig bond0 192.168.1.2 netmask 255.255.255.0 up
>ifenslave bond0 eth0
>ifenslave bond0 eth1
>ifenslave bond0 eth2
>ping 192.168.1.100 -A -s 10240
>
>I find that bonding will always use eth0 and eth1, it never uses eth2,
>because tlb_get_least_loaded_slave() always chooses slave from
>bonding->first_slave, that gives the beginnig slaves more chances to be
>used.
>
>Do you think this is a problem ?

	Not for this test case, no.

	On the other hand, if you run three pings concurrently to three
different destinations and it still never uses eth2, then that might be
something to look into.

>Does it has conflicts with the meaning of balance and reblance?

	Not really; with only one active flow, there isn't really any
advantage to moving it around.  The balance and rebalance activity
becomes more interesting when the traffic volume and number of
destinations is larger.

	-J

>>> Signed-off-by: Weiping Pan(潘卫平)<[email-masked]>
>>> ---
>>> drivers/net/bonding/bond_alb.c |   17 +++++++++++++++--
>>> 1 files changed, 15 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>>> index 9bc5de3..9fa64b0 100644
>>> --- a/drivers/net/bonding/bond_alb.c
>>> +++ b/drivers/net/bonding/bond_alb.c
>>> @@ -36,6 +36,7 @@
>>> #include<linux/if_bonding.h>
>>> #include<linux/if_vlan.h>
>>> #include<linux/in.h>
>>> +#include<linux/random.h>
>>> #include<net/ipx.h>
>>> #include<net/arp.h>
>>> #include<net/ipv6.h>
>>> @@ -206,15 +207,27 @@ static long long compute_gap(struct slave *slave)
>>> /* Caller must hold bond lock for read */
>>> static struct slave *tlb_get_least_loaded_slave(struct bonding *bond)
>>> {
>>> -	struct slave *slave, *least_loaded;
>>> +	struct slave *slave, *least_loaded, *start_slave;
>>> 	long long max_gap;
>>> 	int i;
>>> +	u8 n;
>>>
>>> 	least_loaded = NULL;
>>> +	start_slave = bond->first_slave;
>>> 	max_gap = LLONG_MIN;
>>> +
>>> +	get_random_bytes(&n, 1);
>>> +
>>> +	if (bond->slave_cnt == 0)
>>> +		return NULL;
>>> +	n = n % bond->slave_cnt;
>>> +
>>> +	for (i=0; i<n; ++i) {
>>> +		start_slave = start_slave->next;
>>> +	}
>>>
>>> 	/* Find the slave with the largest gap */
>>> -	bond_for_each_slave(bond, slave, i) {
>>> +	bond_for_each_slave_from(bond, slave, i, start_slave) {
>>> 		if (SLAVE_IS_OK(slave)) {
>>> 			long long gap = compute_gap(slave);
>>>
>>> -- 
>>> 1.7.4

---
	-Jay Vosburgh, IBM Linux Technology Center, [email-masked]