Re: [PATCH] net: bonding: Fix transmit load balancing in balance-alb mode if specified by sysfs

On 08/09/17 05:06, Kosuke Tatsukawa wrote:

Hi,

quoted

On  7.09.2017 01:47, Kosuke Tatsukawa wrote:

quoted

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 <redacted>
Signed-off-by: Kosuke Tatsukawa <redacted>
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.

quoted

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

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.

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",