netdev - Re: Socket buffer sizes with autotuning

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Message-ID: <d1c2719f0805161813kc0dca29y1feaf4d512a959e@mail.gmail.com>
Date:	Fri, 16 May 2008 18:13:20 -0700
From:	"Jerry Chu" <hkchu@...gle.com>
To:	"David Miller" <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: Socket buffer sizes with autotuning

Ok, now the code seems to work when TSO is disabled, i.e., cwnd
remains low (40-60pkts) and only grows slowly for extended period on
a back2back 1GbE link. It also works when tcpdump was running
after I fixed the code, per your suggestion, to only bump the in_flight
count for fast clones.

But it doesn't work when TSO is enabled. I've fixed tso_fragment() to
correctly set skb_shinfo(buff)->in_flight after the split. But cwnd still
grows rapidly to a few hundred pkts (although smaller than w/o
the fix). The host inflight accounting gets screwed up. It looks like
pskb_expand_head() called by tcp_tso_acked()->tcp_trim_head()
messes up the accounting but I don't know how to fix it (still trying
to understand this complex piece of code). There could be other
reason as well.

Jerry

On Mon, May 12, 2008 at 9:02 PM, David Miller <davem@...emloft.net> wrote:
> From: "Jerry Chu" <hkchu@...gle.com>
> Date: Mon, 12 May 2008 21:00:08 -0700
>
>> Does xchg() return the old value? (Can't find any comments on it.)
>
> Yes, otherwise it wouldn't be very useful.
>
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