netdev - Re: [PATCH v5] rfs: Receive Flow Steering

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Date:	Sat, 17 Apr 2010 10:38:25 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v5] rfs: Receive Flow Steering

>
> With attached patch, I reached
>
> Throughput 4465.13 MB/sec 16 procs
>
> RFS better than no RPS/RFS :)
>
> So, the old idea to make rxhash consistent (same value in both
> directions) is a win for some workloads (Consider connection tracking /
> firewalling)
>
> port1 = ...
> port2 = ...
> addr1 = ...
> addr2 = ...
> if (addr1 > addr2)
>        exchange(addr1, addr2)
> if (port1 > port2)
>        exchange(port, port2)
>
> hash = jhash(addr1, addr2, (port1<<16)+port2, ...)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 7abf959..6b757ff 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2280,8 +2280,10 @@ static int get_rps_cpu(struct net_device *dev,
> struct sk_buff *skb,
>        case IPPROTO_AH:
>        case IPPROTO_SCTP:
>        case IPPROTO_UDPLITE:
> -               if (pskb_may_pull(skb, (ihl * 4) + 4))
> -                       ports = *((u32 *) (skb->data + (ihl * 4)));
> +               if (pskb_may_pull(skb, (ihl * 4) + 4)) {
> +                       u16 *_ports = (u16 *)(skb->data + (ihl * 4));
> +                       ports = _ports[0] ^ _ports[1];
> +               }
>                break;
>
>        default:
>
That's cool!, but I still like the idea that this hash is treated as
an opaque value, getting the hash from the device to avoid the jhash
or cache misses on the packet can also be a win...  Maybe connection
tracking/firewall could use the skb->rxhash which provides the
consistency and also eliminates the need to do more jhashes.


>
>
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