netdev - Re: [PATCH net-next v4] rps: selective flow shedding during softnet overflow

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Date:	Tue, 23 Apr 2013 19:11:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	Willem de Bruijn <willemb@...gle.com>,
	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net-next v4] rps: selective flow shedding during softnet
 overflow

On Tue, 2013-04-23 at 21:44 -0400, Jamal Hadi Salim wrote:

> 
> BTW, looking at __skb_get_rxhash(), if i had a driver that sets either
> skb->rxhash (picks it off the dma descriptor), could i not use that 
> instead of computing the hash? something like attached patch.
> 

The caller does this already ;)

static inline __u32 skb_get_rxhash(struct sk_buff *skb)
{
        if (!skb->l4_rxhash)
                __skb_get_rxhash(skb);

        return skb->rxhash;
}

Rationale being : if l4 rxhash was already provided, use it.

AFAIK, only bnx2x provides this.

For other cases, we prefer trying a software rxhash, as it gives us more
capabilities than the standard Toepliz hash (Not l4 for UDP flows for
example)



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