netdev - Re: [PATCH net-next] tcp: do not pace pure ack packets

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Message-ID: <1424010339.4942.31.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 15 Feb 2015 06:25:39 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Kenneth Klette Jonassen <kennetkl@....uio.no>,
	john fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH net-next] tcp: do not pace pure ack packets

On Sat, 2015-02-14 at 22:45 +0200, Or Gerlitz wrote:

> Wow, so what is the black box impact on systems running without the
> fix, pacing works but also un-needed slow downs
> are introduced, right?
> 
> Sounds to me as something we really want to push into -stable, isn't that?
> 
> Do you think we need to let the patch rot for a while in 3.20-rc or we
> can do it right away?

No impact at all. black box are forwarding packets, they are not pacing
them at all.

fq/pacing paces locally generated traffic only.

This works the following way :

TCP sets sk->sk_pacing_rate = 2 * cwnd * mss / srtt

fq then paces packets that are attached to a (local) socket, and where
sk->sk_pacing_rate is different than default value ( ~0U )

The only case a middle box could pace is when/if the optional 
'maxrate xxx' parameter is given to fq packet scheduler, and in this
case the intent is to have a max rate, including ACK packets.

I really do not think this patch is a stable candidate.

Thanks


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