netdev - Re: [PATCH v2 net-next 0/3] net: Add incoming CPU mask to sockets

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Message-ID: <1432680153.4060.304.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 26 May 2015 15:42:33 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 0/3] net: Add incoming CPU mask to sockets

On Tue, 2015-05-26 at 13:01 -0700, Tom Herbert wrote:

> In that case there's no guarantee that any two packets in a flow will
> hit the same CPU so there's no way to establish affinity to the
> interrupt anyway. RFS would work okay to get affinity of the soft
> processing, but there would be no point in trying to do any affinity
> with incoming cpu so this feature wouldn't help.

This is why I think this patch can hurt users.

RPS/RFS/smp_affinity/SO_REUSEPORT/cpuhotplug are only hints, that would
never break TCP session establishment, even with hash collisions and
sockets being added/deleted to SO_REUSEPORT pools.

It works in _all_ situations. Even the crazy/stupid setups.

Your patch is breaking this rule, without any clear documentation on how
to make sure everything is properly setup.

I am not sure my tcp listener stuff will be finished for 4.2, because I
had to spend lot of time to more urgent stuff lately, like reviewing
patches ;)

I would prefer your patch is added for 4.3, not before.


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