netdev - Re: [PATCH] RPS: support 802.1q and pppoe session

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Date:	Thu, 25 Mar 2010 13:12:57 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] RPS: support 802.1q and pppoe session

On Thu, Mar 25, 2010 at 1:03 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> While this might sounds a good idea, you really should split this in two
> parts.
>
> By the way, why not handling IPIP too ?

I'm not sure if it is a good idea to support VLAN and PPPOE, and
actually David don't like it. :(

>
> Because I believe 802.1q part has no added value for instance, since
> packet handled by CPUX will be decoded and passed to VLAN device, having
> a chance to be fully taken by RPS, since we go back to netif_rx().
>
> Probably same thing for IPIP / PPPOE can be discussed.

It is useful when Linux is run as a bridge.

>
> I agree we might need a flag or something to reset rxhash to 0 somewhere
> (probably in non accelerated vlan rx handling) to force second
> get_rps_cpu() invocation to recompute it. This small correction has no
> cost if put outside of get_rps_cpus().
>
> If get_rps_cpus() is too complex, it might become too slow for typical
> use. We should find smart ways to solve your performance problem if they
> ever exist.
>

It means that more than one IPI will be sent for just a single
packets, I don't think the cost is acceptable.

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