netdev - Re: [PATCH v5] rps: Receive Packet Steering

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Date:	Fri, 15 Jan 2010 17:20:43 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, therbert@...gle.com,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH v5] rps: Receive Packet Steering

On Fri, Jan 15, 2010 at 4:49 PM, David Miller <davem@...emloft.net> wrote:
>
> Actually, no thanks.  Have you actually taken a look at
> ipv6_skip_exthdr()?
>
> Do that, then tell me that you want the extra function call, plus all
> of the processing and data touching that that function does, just to
> handle the case that there "might" be ipv6 extension headers there.
>

I don't think ipv6_skip_exthdr() is too weight. If there isn't any
extra header, only some compare and jump instruments are added, and no
more data references. If there are some headers, I think distributing
packets among CPUs is more important than the extra cost introduced by
calling ipv6_skip_exthdr().

> It is the exception rather than the rule, and I think it's just
> assume we have a real protocol header next.
>
> And that's what skb_tx_hash() used to do too before we started using
> the recorded RX queue and socket hash values.
>
> Nobody cared and nobody complained.  Guess why?  Because in practice
> it doesn't matter.
>

Maybe they don't know it.If it was a performance regression, I think
more people might pay attention on it.

-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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