netdev - Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive for TCP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1335213446.5205.65.camel@edumazet-glaptop>
Date:	Mon, 23 Apr 2012 22:37:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	rick.jones2@...com, netdev@...r.kernel.org, therbert@...gle.com,
	ncardwell@...gle.com, maze@...gle.com, ycheng@...gle.com,
	ilpo.jarvinen@...sinki.fi
Subject: Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive
 for TCP

On Mon, 2012-04-23 at 16:01 -0400, David Miller wrote:

> Hmmm... why don't we just acknowledge reality and special case ACKs?
> 

Yes why not.


> If a TCP packet is dataless we should just let it go through no matter
> what and with no limits.  It is by definition transient and will not
> get queued up into the socket past this backlog stage.
> 

Even being transient we need a limit. Without copybreak, an ACK can cost
2048+256 bytes.

In my 10Gbit tests (standard netperf using 16K buffers), I've seen
backlogs of 300 ACK packets...

> This proposed patch allows non-dataless packets to eat more space in
> the backlog, thus the concern and slight pushback.  And from another
> perspective, having the stack process data packets which will just
> get dropped when we try to attach it to the receive queue is just
> wasted work.

We could try to coalesce ACKs before backlogging them. I'll work on
this.

Thanks


--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html