netdev - Re: [PATCH net-next v2 1/1] net: openvswitch: Use on stack sw_flow_key in ovs_packet_cmd

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Date:   Thu, 23 Feb 2023 20:24:50 +0800
From:   Eddy Tao <taoyuan_eddy@...mail.com>
To:     netdev@...r.kernel.org
Cc:     Pravin B Shelar <pshelar@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, dev@...nvswitch.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 1/1] net: openvswitch: Use on stack
 sw_flow_key in ovs_packet_cmd_execute

Sorry, there is a typo in the mail, i will resend shortly, please ignore 
it for now

On 2023/2/23 20:21, Eddy Tao wrote:
> Use on stack sw_flow_key in ovs_packet_cmd_execute
>
> Reason: As key function in slow-path, ovs_packet_cmd_execute and
>          ovs_flow_cmd_new allocate transient memory for sw_flow
>          and frees it at the end of function.
>          The procedure is not efficient in 2 aspects
>          1. actuall sw_flow_key is what the function need
>          2. free/alloc involves kmem_cache operations
>          when system under frequent slow path operation
>
>          Existing code in ovs_flow_cmd_new/set/get use stack
>          to store sw_flow_mask and sw_flow_key deliberately
>
> Performance benefit:
>          ovs_packet_cmd_execute efficiency improved
>          Avoid 2 calls to kmem_cache alloc
>          Avoid memzero of 200 bytes
>          6% less instructions
>
> Testing topology
>              +-----+
>        nic1--|     |--nic1
>        nic2--|     |--nic2
> VM1(16cpus) | ovs |   VM2(16 cpus)
>        nic3--|4cpus|--nic3
>        nic4--|     |--nic4
>              +-----+
>     2 threads on each vnic with affinity set on client side
>
> netperf -H $peer -p $((port+$i)) -t UDP_RR  -l 60 -- -R 1 -r 8K,8K
> netperf -H $peer -p $((port+$i)) -t TCP_RR  -l 60 -- -R 1 -r 120,240
> netperf -H $peer -p $((port+$i)) -t TCP_CRR -l 60 -- -R 1 -r 120,240
>
> Before the fix
>        Mode Iterations   Variance    Average
>      UDP_RR         10      %1.31      46724
>      TCP_RR         10      %6.26      77188
>     TCP_CRR         10      %0.10      20505
> UDP_STREAM         10      %4.55      19907
> TCP_STREAM         10      %9.93      28942
>
> After the fix
>        Mode Iterations   Variance    Average
>      UDP_RR         10      %1.51      49097
>      TCP_RR         10      %5.58      78540
>     TCP_CRR         10      %0.14      20542
> UDP_STREAM         10     %11.17      22532
> TCP_STREAM         10     %11.14      28579
>
> Signed-off-by: Eddy Tao <taoyuan_eddy@...mail.com>
> ---
>   V1 -> V2: Further reduce memory usage by using sw_flow_key instead
>             of sw_flow, revise description of change and provide data
>
>   net/openvswitch/datapath.c | 30 +++++++++++-------------------
>   1 file changed, 11 insertions(+), 19 deletions(-)
>
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index fcee6012293b..ae3146d51079 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -596,8 +596,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
>   	struct nlattr **a = info->attrs;
>   	struct sw_flow_actions *acts;
>   	struct sk_buff *packet;
> -	struct sw_flow *flow;
> -	struct sw_flow_actions *sf_acts;
> +	struct sw_flow_key key;
>   	struct datapath *dp;
>   	struct vport *input_vport;
>   	u16 mru = 0;
> @@ -636,24 +635,20 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
>   	}
>   
>   	/* Build an sw_flow for sending this packet. */
> -	flow = ovs_flow_alloc();
> -	err = PTR_ERR(flow);
> -	if (IS_ERR(flow))
> -		goto err_kfree_skb;
> +	memset(&key, 0, sizeof(key));
>   
>   	err = ovs_flow_key_extract_userspace(net, a[OVS_PACKET_ATTR_KEY],
> -					     packet, &flow->key, log);
> +					     packet, &key, log);
>   	if (err)
> -		goto err_flow_free;
> +		goto err_kfree_skb;
>   
>   	err = ovs_nla_copy_actions(net, a[OVS_PACKET_ATTR_ACTIONS],
> -				   &flow->key, &acts, log);
> +				   &key, &acts, log);
>   	if (err)
> -		goto err_flow_free;
> +		goto err_kfree_skb;
>   
> -	rcu_assign_pointer(flow->sf_acts, acts);
> -	packet->priority = flow->key.phy.priority;
> -	packet->mark = flow->key.phy.skb_mark;
> +	packet->priority = key.phy.priority;
> +	packet->mark = key.phy.skb_mark;
>   
>   	rcu_read_lock();
>   	dp = get_dp_rcu(net, ovs_header->dp_ifindex);
> @@ -661,7 +656,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
>   	if (!dp)
>   		goto err_unlock;
>   
> -	input_vport = ovs_vport_rcu(dp, flow->key.phy.in_port);
> +	input_vport = ovs_vport_rcu(dp, key.phy.in_port);
>   	if (!input_vport)
>   		input_vport = ovs_vport_rcu(dp, OVSP_LOCAL);
>   
> @@ -670,20 +665,17 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
>   
>   	packet->dev = input_vport->dev;
>   	OVS_CB(packet)->input_vport = input_vport;
> -	sf_acts = rcu_dereference(flow->sf_acts);
>   
>   	local_bh_disable();
> -	err = ovs_execute_actions(dp, packet, sf_acts, &flow->key);
> +	err = ovs_execute_actions(dp, packet, acts, &key);
>   	local_bh_enable();
>   	rcu_read_unlock();
>   
> -	ovs_flow_free(flow, false);
> +	ovs_nla_free_flow_actions(acts);
>   	return err;
>   
>   err_unlock:
>   	rcu_read_unlock();
> -err_flow_free:
> -	ovs_flow_free(flow, false);
>   err_kfree_skb:
>   	kfree_skb(packet);
>   err: