Message-ID: <CAF2d9jgHLJ28hpiSafL7823-Ga4y8aYZ2t_Sqh7D51VL_DgDww@mail.gmail.com>
Date:   Fri, 8 Sep 2017 16:54:48 -0700
From:   Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     Kosuke Tatsukawa <tatsu@...jp.nec.com>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Reinis Rozitis <r@...e.lv>
Subject: Re: [PATCH] net: bonding: Fix transmit load balancing in balance-alb
 mode if specified by sysfs

On Fri, Sep 8, 2017 at 7:30 AM, Nikolay Aleksandrov
<nikolay@...ulusnetworks.com> wrote:
> On 08/09/17 17:17, Kosuke Tatsukawa wrote:
>> Hi,
>>
>>> On 08/09/17 13:10, Nikolay Aleksandrov wrote:
>>>> On 08/09/17 05:06, Kosuke Tatsukawa wrote:
>>>>> 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@...e.lv>
>>>>>>> Signed-off-by: Kosuke Tatsukawa <tatsu@...jp.nec.com>
>>>>>>> Cc: stable@...r.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@...jp.nec.com
>>>>>
>>>>
>>>> Logically the approach looks good, that being said it adds unnecessary tests in
>>>> the fast path, why not just something like the patch below ? That only leaves the
>>>> problem if it is zeroed in TLB and switched to ALB mode, and that is a one line
>>>> fix to unsuppmodes just allow it to be set for that specific case. The below
>>>> returns the default behaviour before the commit in your Fixes tag.
>>>>
>>>>
>>>
>>> Actually I'm fine with your approach, too. It will fix this regardless of the
>>> value of tlb_dynamic_lb which sounds good to me for the price of a test in
>>> the fast path.
>>
>> If you're concerned about the additional test in the fast path, how
>> about the patch below.  I've added an arguemnt to bond_do_alb_xmit()
>> to handle both balance-tlb and balance-alb similary.
>>
>
> Even better, looks great! 1 question below though.
>
>> I'm not sure if this causes any problem if tlb_dynamic_lb is changed
>> while calling bond_do_alb_xmit() in balance-tlb mode.
>
> The option has the ifdown flag, you shouldn't be able to change it while
> the bond dev is up, but even if you could I don't think it will be an issue
> for the xmit.
>
>> ---
>> Kosuke TATSUKAWA  | 1st Platform Software Division
>>                   | NEC Solution Innovators
>>                   | tatsu@...jp.nec.com
>>
>> ------------------------------------------------------------------------
>>  drivers/net/bonding/bond_alb.c  |   11 ++++++-----
>>  drivers/net/bonding/bond_main.c |    5 +++--
>>  2 files changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>> index c02cc81..7710f20 100644
>> --- a/drivers/net/bonding/bond_alb.c
>> +++ b/drivers/net/bonding/bond_alb.c
>> @@ -1317,7 +1317,7 @@ void bond_alb_deinitialize(struct bonding *bond)
>>  }
>>
>>  static int bond_do_alb_xmit(struct sk_buff *skb, struct bonding *bond,
>> -                         struct slave *tx_slave)
>> +                         struct slave *tx_slave, int tlb_dynamic_lb)
>>  {
>>       struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>>       struct ethhdr *eth_data = eth_hdr(skb);
>> @@ -1325,7 +1325,7 @@ 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 (tlb_dynamic_lb)
>>                       bond_info->unbalanced_load += skb->len;
>>       }
>>
>> @@ -1339,7 +1339,7 @@ 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 && tlb_dynamic_lb) {
>>               spin_lock(&bond->mode_lock);
>>               __tlb_clear_slave(bond, tx_slave, 0);
>>               spin_unlock(&bond->mode_lock);
>> @@ -1386,7 +1386,8 @@ int bond_tlb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>>                       break;
>>               }
>>       }
>> -     return bond_do_alb_xmit(skb, bond, tx_slave);
>> +     return bond_do_alb_xmit(skb, bond, tx_slave,
>> +                             bond->params.tlb_dynamic_lb);
>>  }
>>
>>  int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>> @@ -1483,7 +1484,7 @@ int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>>               tx_slave = tlb_choose_channel(bond, hash_index, skb->len);
>>       }
>>
>> -     return bond_do_alb_xmit(skb, bond, tx_slave);
>> +     return bond_do_alb_xmit(skb, bond, tx_slave, 1);
>>  }
>>
>>  void bond_alb_monitor(struct work_struct *work)
>> 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_TLB))
>
> mode == tlb ? shouldn't this check be for alb ?
>
Actually this is not needed since this is already inside if
(bond_is_lb()) condition.

>>                       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);
>>
>
I think the underlying issue is that tlb_dynamic_lb should be set to 1
for all modes which was not the case when it was getting initialized
only forTLB mode. So from that perspective I prefer Nik's patch with a
small variation that guards the case when mode transitions from TLB to
ALB. The reason why I like that patch is because it's simple and
avoids complications.

Here is what I meant -

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index fc63992ab0e0..c99dc59d729b 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -4289,7 +4289,7 @@ static int bond_check_params(struct bond_params *params)
        int bond_mode   = BOND_MODE_ROUNDROBIN;
        int xmit_hashtype = BOND_XMIT_POLICY_LAYER2;
        int lacp_fast = 0;
-       int tlb_dynamic_lb = 0;
+       int tlb_dynamic_lb;

        /* Convert string parameters. */
        if (mode) {
@@ -4601,16 +4601,13 @@ 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)) {
-               bond_opt_initstr(&newval, "default");
-               valptr = bond_opt_parse(bond_opt_get(BOND_OPT_TLB_DYNAMIC_LB),
-                                       &newval);
-               if (!valptr) {
-                       pr_err("Error: No tlb_dynamic_lb default value");
-                       return -EINVAL;
-               }
-               tlb_dynamic_lb = valptr->value;
+       bond_opt_initstr(&newval, "default");
+       valptr = bond_opt_parse(bond_opt_get(BOND_OPT_TLB_DYNAMIC_LB), &newval);
+       if (!valptr) {
+               pr_err("Error: No tlb_dynamic_lb default value");
+               return -EINVAL;
        }
+       tlb_dynamic_lb = valptr->value;

        if (lp_interval == 0) {
                pr_warn("Warning: ip_interval must be between 1 and
%d, so it was reset to %d\n",
diff --git a/drivers/net/bonding/bond_options.c
b/drivers/net/bonding/bond_options.c
index a12d603d41c6..7feacd262182 100644
--- a/drivers/net/bonding/bond_options.c
+++ b/drivers/net/bonding/bond_options.c
@@ -754,6 +754,12 @@ static int bond_option_mode_set(struct bonding *bond,
                           bond->params.miimon);
        }

+       /* Guard against transition TLB/tlb_dynamic_lb=0 -> ALB mode.
+        * In ALB mode, tlb_dynamic_lb must be set to 1.
+        */
+       if (newval->value == BOND_MODE_ALB && bond->params.tlb_dynamic_lb != 1)
+               bond->params.tlb_dynamic_lb = 1;
+
        /* don't cache arp_validate between modes */
        bond->params.arp_validate = BOND_ARP_VALIDATE_NONE;
        bond->params.mode = newval->value;

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