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SubjectRe: [PATCH] net: bonding: Fix transmit load balancing in balance-alb mode if specified by sysfs
Date
Hi,

> On 7.09.2017 01:47, Kosuke Tatsukawa wrote:
>> Commit cbf5ecb30560 ("net: bonding: Fix transmit load balancing in
>> balance-alb mode") tried to fix transmit dynamic load balancing in
>> balance-alb mode, which wasn't working after commit 8b426dc54cf4
>> ("bonding: remove hardcoded value").
>>
>> It turned out that my previous patch only fixed the case when
>> balance-alb was specified as bonding module parameter, and not when
>> balance-alb mode was set using /sys/class/net/*/bonding/mode (the most
>> common usage). In the latter case, tlb_dynamic_lb was set up according
>> to the default mode of the bonding interface, which happens to be
>> balance-rr.
>>
>> This additional patch addresses this issue by setting up tlb_dynamic_lb
>> to 1 if "mode" is set to balance-alb through the sysfs interface.
>>
>> I didn't add code to change tlb_balance_lb back to the default value for
>> other modes, because "mode" is usually set up only once during
>> initialization, and it's not worthwhile to change the static variable
>> bonding_defaults in bond_main.c to a global variable just for this
>> purpose.
>>
>> Commit 8b426dc54cf4 also changes the value of tlb_dynamic_lb for
>> balance-tlb mode if it is set up using the sysfs interface. I didn't
>> change that behavior, because the value of tlb_balance_lb can be changed
>> using the sysfs interface for balance-tlb, and I didn't like changing
>> the default value back and forth for balance-tlb.
>>
>> As for balance-alb, /sys/class/net/*/bonding/tlb_balance_lb cannot be
>> written to. However, I think balance-alb with tlb_dynamic_lb set to 0
>> is not an intended usage, so there is little use making it writable at
>> this moment.
>>
>> Fixes: 8b426dc54cf4 ("bonding: remove hardcoded value")
>> Reported-by: Reinis Rozitis <r@roze.lv>
>> Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
>> Cc: stable@vger.kernel.org # v4.12+
>> ---
>> drivers/net/bonding/bond_options.c | 3 +++
>> 1 files changed, 3 insertions(+), 0 deletions(-)
>>
>
> I don't believe this to be the right solution, hardcoding it like this
> changes user-visible behaviour. The issue is that if someone configured
> it to be 0 in tlb mode, suddenly it will become 1 and will silently
> override their config if they switch the mode to alb. Also it robs users
> from their choice.
>
> If you think this should be settable in ALB mode, then IMO you should
> edit tlb_dynamic_lb option's unsuppmodes and allow it to be set in ALB.
> That would also be consistent with how it's handled in TLB mode.

No, I don't think tlb_dynamic_lb should be settable in balance-alb at
this point. All the current commits regarding tlb_dynamic_lb are for
balance-tlb mode, so I don't think balance-alb with tlb_dynamic_lb set
to 0 is an intended usage.


> Going back and looking at your previous fix I'd argue that it is also
> wrong, you should've removed the mode check altogether to return the
> original behaviour where the dynamic_lb is set to 1 (enabled) by
> default and then ALB mode would've had it, of course that would've left
> the case of setting it to 0 in TLB mode and switching to ALB, but that
> is a different issue.

Maybe balance-alb shouldn't be dependent on tlb_dynamic_lb.
tlb_dynamic_lb is referenced in the following functions.

+ bond_do_alb_xmit() -- Used by both balance-tlb and balance-alb
+ bond_tlb_xmit() -- Only used by balance-tlb
+ bond_open() -- Used by both balance-tlb and balance-alb
+ bond_check_params() -- Used during module initialization
+ bond_fill_info() -- Used to get/set value
+ bond_option_tlb_dynamic_lb_set() -- Used to get/set value
+ bonding_show_tlb_dynamic_lb() -- Used to get/set value
+ bond_is_nondyn_tlb() -- Only referenced if balance-tlb mode

The following untested patch adds code to make balance-alb work as if
tlb_dynamic_lb==1 for the functions which affect balance-alb mode. It
also reverts my previous patch.

What do you think about this approach?
---
Kosuke TATSUKAWA | 1st Platform Software Division
| NEC Solution Innovators
| tatsu@ab.jp.nec.com

------------------------------------------------------------------------
drivers/net/bonding/bond_alb.c | 6 ++++--
drivers/net/bonding/bond_main.c | 5 +++--
2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
index c02cc81..a9229b5 100644
--- a/drivers/net/bonding/bond_alb.c
+++ b/drivers/net/bonding/bond_alb.c
@@ -1325,7 +1325,8 @@ static int bond_do_alb_xmit(struct sk_buff *skb, struct bonding *bond,
if (!tx_slave) {
/* unbalanced or unassigned, send through primary */
tx_slave = rcu_dereference(bond->curr_active_slave);
- if (bond->params.tlb_dynamic_lb)
+ if (bond->params.tlb_dynamic_lb ||
+ (BOND_MODE(bond) == BOND_MODE_ALB))
bond_info->unbalanced_load += skb->len;
}

@@ -1339,7 +1340,8 @@ static int bond_do_alb_xmit(struct sk_buff *skb, struct bonding *bond,
goto out;
}

- if (tx_slave && bond->params.tlb_dynamic_lb) {
+ if (tx_slave && (bond->params.tlb_dynamic_lb ||
+ BOND_MODE(bond) == BOND_MODE_ALB)) {
spin_lock(&bond->mode_lock);
__tlb_clear_slave(bond, tx_slave, 0);
spin_unlock(&bond->mode_lock);
diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index fc63992..bcb71e7 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -3305,7 +3305,8 @@ static int bond_open(struct net_device *bond_dev)
*/
if (bond_alb_initialize(bond, (BOND_MODE(bond) == BOND_MODE_ALB)))
return -ENOMEM;
- if (bond->params.tlb_dynamic_lb)
+ if (bond->params.tlb_dynamic_lb ||
+ (BOND_MODE(bond) == BOND_MODE_ALB))
queue_delayed_work(bond->wq, &bond->alb_work, 0);
}

@@ -4601,7 +4602,7 @@ static int bond_check_params(struct bond_params *params)
}
ad_user_port_key = valptr->value;

- if ((bond_mode == BOND_MODE_TLB) || (bond_mode == BOND_MODE_ALB)) {
+ if (bond_mode == BOND_MODE_TLB) {
bond_opt_initstr(&newval, "default");
valptr = bond_opt_parse(bond_opt_get(BOND_OPT_TLB_DYNAMIC_LB),
&newval);
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