Subject: Re: [PATCH v7 net-next 2/2] bonding: Simplify the xmit function for modes that use xmit_hash

From: Nikolay Aleksandrov <[email-masked]>
Date: Sat, 04 Oct 2014 09:37:37 +0200

On 10/04/2014 02:48 AM, Mahesh Bandewar wrote:
> Earlier change to use usable slave array for TLB mode had an additional
> performance advantage. So extending the same logic to all other modes
> that use xmit-hash for slave selection (viz 802.3AD, and XOR modes).
> Also consolidating this with the earlier TLB change.
> 
> The main idea is to build the usable slaves array in the control path
> and use that array for slave selection during xmit operation.
> 
> Measured performance in a setup with a bond of 4x1G NICs with 200
> instances of netperf for the modes involved (3ad, xor, tlb)
> cmd: netperf -t TCP_RR -H <TargetHost> -l 60 -s 5
> 
> Mode        TPS-Before   TPS-After
> 
> 802.3ad   : 468,694      493,101
> TLB (lb=0): 392,583      392,965
> XOR       : 475,696      484,517
> 
> Signed-off-by: Mahesh Bandewar <[email-masked]>
> Signed-off-by: Nikolay Aleksandrov <[email-masked]>
> ---
> v1:
>   (a) If bond_update_slave_arr() fails to allocate memory, it will overwrite
>       the slave that need to be removed.
>   (b) Freeing of array will assign NULL (to handle bond->down to bond->up
>       transition gracefully.
>   (c) Change from pr_debug() to pr_err() if bond_update_slave_arr() returns
>       failure.
>   (d) XOR: bond_update_slave_arr() will consider mii-mon, arp-mon cases and
>       will populate the array even if these parameters are not used.
>   (e) 3AD: Should handle the ad_agg_selection_logic correctly.
> v2:
>   (a) Removed rcu_read_{un}lock() calls from array manipulation code.
>   (b) Slave link-events now refresh array for all these modes.
>   (c) Moved free-array call from bond_close() to bond_uninit().
> v3:
>   (a) Fixed null pointer dereference.
>   (b) Removed bond->lock lockdep dependency.
> v4:
>   (a) Made to changes to comply with Nikolay's locking changes
>   (b) Added a work-queue to refresh slave-array when RTNL is not held
>   (c) Array refresh happens ONLY with RTNL now.
>   (d) alloc changed from GFP_ATOMIC to GFP_KERNEL
> v5:
>   (a) Consolidated all delayed slave-array updates at one place in
>       3ad_state_machine_handler()
> v6:
>   (a) Free slave array when there is no active aggregator
> v7:
>   (a) Couple of trivial changes.
> 
>  drivers/net/bonding/bond_3ad.c  | 140 +++++++++++------------------
>  drivers/net/bonding/bond_alb.c  |  51 ++---------
>  drivers/net/bonding/bond_alb.h  |   8 --
>  drivers/net/bonding/bond_main.c | 192 +++++++++++++++++++++++++++++++++++++---
>  drivers/net/bonding/bonding.h   |  10 +++
>  5 files changed, 249 insertions(+), 152 deletions(-)
> 
<<<snip>>>
> +/* Build the usable slaves array in control path for modes that use xmit-hash
> + * to determine the slave interface -
> + * (a) BOND_MODE_8023AD
> + * (b) BOND_MODE_XOR
> + * (c) BOND_MODE_TLB && tlb_dynamic_lb == 0
> + *
> + * The caller is expected to hold RTNL only and NO other lock!
> + */
> +int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave)
> +{
> +	struct slave *slave;
> +	struct list_head *iter;
> +	struct bond_up_slave *new_arr, *old_arr;
> +	int slaves_in_agg;
> +	int agg_id = 0;
> +	int ret = 0;
> +
> +#ifdef CONFIG_LOCKDEP
> +	lockdep_assert_held(&bond->mode_lock);
> +#endif
^^^^^^^^^
This is wrong now, the logic is inverted.
It will WARN every time mode_lock is _not_ held:

#define lockdep_assert_held(l)  do {                            \
                WARN_ON(debug_locks && !lockdep_is_held(l));    \
        } while (0)

The previous version was correct which did a WARN when mode_lock was
actually held as that is the wrong condition, not when it's not held.
I've missed that comment earlier.

(also switched Veaceslav's email address with the correct one in the CC list)

> +
> +	new_arr = kzalloc(offsetof(struct bond_up_slave, arr[bond->slave_cnt]),
> +			  GFP_KERNEL);
> +	if (!new_arr) {
> +		ret = -ENOMEM;
> +		pr_err("Failed to build slave-array.\n");
> +		goto out;
> +	}
> +	if (BOND_MODE(bond) == BOND_MODE_8023AD) {
> +		struct ad_info ad_info;
> +
> +		if (bond_3ad_get_active_agg_info(bond, &ad_info)) {
> +			pr_debug("bond_3ad_get_active_agg_info failed\n");
> +			kfree_rcu(new_arr, rcu);
> +			/* No active aggragator means it's not safe to use
> +			 * the previous array.
> +			 */
> +			old_arr = rtnl_dereference(bond->slave_arr);
> +			if (old_arr) {
> +				RCU_INIT_POINTER(bond->slave_arr, NULL);
> +				kfree_rcu(old_arr, rcu);
> +			}
> +			goto out;
> +		}
> +		slaves_in_agg = ad_info.ports;
> +		agg_id = ad_info.aggregator_id;
> +	}
> +	bond_for_each_slave(bond, slave, iter) {
> +		if (BOND_MODE(bond) == BOND_MODE_8023AD) {
> +			struct aggregator *agg;
> +
> +			agg = SLAVE_AD_INFO(slave)->port.aggregator;
> +			if (!agg || agg->aggregator_identifier != agg_id)
> +				continue;
> +		}
> +		if (!bond_slave_can_tx(slave))
> +			continue;
> +		if (skipslave == slave)
> +			continue;
> +		new_arr->arr[new_arr->count++] = slave;
> +	}
> +
> +	old_arr = rtnl_dereference(bond->slave_arr);
> +	rcu_assign_pointer(bond->slave_arr, new_arr);
> +	if (old_arr)
> +		kfree_rcu(old_arr, rcu);
> +out:
> +	if (ret != 0 && skipslave) {
> +		int idx;
> +
> +		/* Rare situation where caller has asked to skip a specific
> +		 * slave but allocation failed (most likely!). BTW this is
> +		 * only possible when the call is initiated from
> +		 * __bond_release_one(). In this situation; overwrite the
> +		 * skipslave entry in the array with the last entry from the
> +		 * array to avoid a situation where the xmit path may choose
> +		 * this to-be-skipped slave to send a packet out.
> +		 */
> +		old_arr = rtnl_dereference(bond->slave_arr);
> +		for (idx = 0; idx < old_arr->count; idx++) {
> +			if (skipslave == old_arr->arr[idx]) {
> +				old_arr->arr[idx] =
> +				    old_arr->arr[old_arr->count-1];
> +				old_arr->count--;
> +				break;
> +			}
> +		}
> +	}
> +	return ret;
> +}
> +
<<<snip>>>