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

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Message-ID: <1269493402.15280.29.camel@edumazet-laptop>
Date:	Thu, 25 Mar 2010 06:03:22 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	xiaosuo@...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

Le jeudi 25 mars 2010 à 12:30 +0800, Changli Gao a écrit :
> support 802.1q and pppoe session
> 
> Support 802.1q and pppoe session, and these two protocols can get the
> benefit from RPS.
> 
> Signed-off-by: Changli Gao <xiaosuo@...il.com>
> ----
> net/core/dev.c | 38 ++++++++++++++++++++++++++++++--------
> 1 file changed, 30 insertions(+), 8 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a03aab4..647ecc4 100644

While this might sounds a good idea, you really should split this in two
parts.

By the way, why not handling IPIP too ?

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.

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.

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