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

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Date:	Sat, 17 Apr 2010 18:10:33 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v5] rfs: Receive Flow Steering

Le vendredi 16 avril 2010 à 23:12 +0200, Eric Dumazet a écrit :
> Le vendredi 16 avril 2010 à 13:42 -0700, Tom Herbert a écrit :
> > On Fri, Apr 16, 2010 at 11:53 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > > Le vendredi 16 avril 2010 à 11:35 -0700, Tom Herbert a écrit :
> > >> Results with "tbench 16" on an 8 core Intel machine.
> > >>
> > >> No RPS/RFS:  2155 MB/sec
> > >> RPS (0ff mask): 1700 MB/sec
> > >> RFS: 1097
> > >>
> > 
> > Blah, I mistakingly reported that... should have been:
> > 
> > No RPS/RFS:  2155 MB/sec
> > RPS (0ff mask): 1097 MB/sec
> > RFS: 1700 MB/sec
> > 
> > Sorry about that!
> 
> > This was my expectation too, and what my "corrected" numbers show :-)
> > But, I take it this is different in your results?
> 
> 
> My results are on a "tbench 16" on an dual X5570  @ 2.93GHz.
> (16 logical cpus)
> 
> No RPS , no RFS : 4448.14 MB/sec 
> RPS : 2298.00 MB/sec (but lot of variation)
> RFS : 2600 MB/sec
> 
> Maybe my RFS setup is bad ?
> (8192 flows)
> 

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:


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