linux-kernel - Re: [PATCH net-next v2 1/4] bonding: add pure source-mac-based tx hashing option

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Date:   Fri, 21 May 2021 16:39:20 +0300
From:   Nikolay Aleksandrov <nikolay@...dia.com>
To:     Jarod Wilson <jarod@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Thomas Davis <tadavis@....gov>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 1/4] bonding: add pure source-mac-based tx
 hashing option

On 21/05/2021 16:27, Jarod Wilson wrote:
> As it turns out, a pure source-mac only tx hash has a place for some VM
> setups. The previously added vlan+srcmac hash doesn't work as well for a
> VM with a single MAC and multiple vlans -- these types of setups path
> traffic more efficiently if the load is split by source mac alone. Enable
> this by way of an extra module parameter, rather than adding yet another
> hashing method in the tx fast path.
> 
> Cc: Jay Vosburgh <j.vosburgh@...il.com>
> Cc: Veaceslav Falico <vfalico@...il.com>
> Cc: Andy Gospodarek <andy@...yhouse.net>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Thomas Davis <tadavis@....gov>
> Cc: Nikolay Aleksandrov <nikolay@...dia.com>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Jarod Wilson <jarod@...hat.com>
> ---
>  Documentation/networking/bonding.rst | 13 +++++++++++++
>  drivers/net/bonding/bond_main.c      | 18 ++++++++++++------
>  2 files changed, 25 insertions(+), 6 deletions(-)
> 

Hi,
You seem to be missing netlink support for the new option. Code-wise the rest seems fine,
my personal preference is still to make a configurable hash option and perhaps default to
srcmac+vlan, i.e. it can be aliased with this hash option. I don't mind either way, but
please add netlink support if it will be a new option as it's the preferred way for
configuring.

Thanks,
 Nik

> diff --git a/Documentation/networking/bonding.rst b/Documentation/networking/bonding.rst
> index 62f2aab8eaec..767dbb49018b 100644
> --- a/Documentation/networking/bonding.rst
> +++ b/Documentation/networking/bonding.rst
> @@ -707,6 +707,13 @@ mode
>  		swapped with the new curr_active_slave that was
>  		chosen.
>  
> +novlan_srcmac
> +
> +	When using the vlan+srcmac xmit_hash_policy, there may be cases where
> +	omitting the vlan from the hash is beneficial. This can be done with
> +	an extra module parameter here. The default value is 0 to include
> +	vlan ID in the transmit hash.
> +
>  num_grat_arp,
>  num_unsol_na
>  
> @@ -964,6 +971,12 @@ xmit_hash_policy
>  
>  		hash = (vlan ID) XOR (source MAC vendor) XOR (source MAC dev)
>  
> +		Optionally, if the module parameter novlan_srcmac=1 is set,
> +		the vlan ID is omitted from the hash and only the source MAC
> +		address is used, reducing the hash to
> +
> +		hash = (source MAC vendor) XOR (source MAC dev)
> +
>  	The default value is layer2.  This option was added in bonding
>  	version 2.6.3.  In earlier versions of bonding, this parameter
>  	does not exist, and the layer2 policy is the only policy.  The
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 20bbda1b36e1..32785e9d0295 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -107,6 +107,7 @@ static char *lacp_rate;
>  static int min_links;
>  static char *ad_select;
>  static char *xmit_hash_policy;
> +static int novlan_srcmac;
>  static int arp_interval;
>  static char *arp_ip_target[BOND_MAX_ARP_TARGETS];
>  static char *arp_validate;
> @@ -168,6 +169,9 @@ MODULE_PARM_DESC(xmit_hash_policy, "balance-alb, balance-tlb, balance-xor, 802.3
>  				   "0 for layer 2 (default), 1 for layer 3+4, "
>  				   "2 for layer 2+3, 3 for encap layer 2+3, "
>  				   "4 for encap layer 3+4, 5 for vlan+srcmac");
> +module_param(novlan_srcmac, int, 0);
> +MODULE_PARM_DESC(novlan_srcmac, "include vlan ID in vlan+srcmac xmit_hash_policy or not; "
> +			      "0 to include it (default), 1 to exclude it");
>  module_param(arp_interval, int, 0);
>  MODULE_PARM_DESC(arp_interval, "arp interval in milliseconds");
>  module_param_array(arp_ip_target, charp, NULL, 0);
> @@ -3523,9 +3527,9 @@ static bool bond_flow_ip(struct sk_buff *skb, struct flow_keys *fk,
>  
>  static u32 bond_vlan_srcmac_hash(struct sk_buff *skb)
>  {
> -	struct ethhdr *mac_hdr = (struct ethhdr *)skb_mac_header(skb);
> +	struct ethhdr *mac_hdr = eth_hdr(skb);
>  	u32 srcmac_vendor = 0, srcmac_dev = 0;
> -	u16 vlan;
> +	u32 hash;
>  	int i;
>  
>  	for (i = 0; i < 3; i++)
> @@ -3534,12 +3538,14 @@ static u32 bond_vlan_srcmac_hash(struct sk_buff *skb)
>  	for (i = 3; i < ETH_ALEN; i++)
>  		srcmac_dev = (srcmac_dev << 8) | mac_hdr->h_source[i];
>  
> -	if (!skb_vlan_tag_present(skb))
> -		return srcmac_vendor ^ srcmac_dev;
> +	hash = srcmac_vendor ^ srcmac_dev;
> +
> +	if (novlan_srcmac || !skb_vlan_tag_present(skb))
> +		return hash;
>  
> -	vlan = skb_vlan_tag_get(skb);
> +	hash ^= skb_vlan_tag_get(skb);
>  
> -	return vlan ^ srcmac_vendor ^ srcmac_dev;
> +	return hash;
>  }
>  
>  /* Extract the appropriate headers based on bond's xmit policy */
>