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Re: bad TSO performance in 2.6.9-rc2-BK

To: "David S. Miller" <davem@xxxxxxxxxxxxx>
Subject: Re: bad TSO performance in 2.6.9-rc2-BK
From: Andi Kleen <ak@xxxxxxx>
Date: Thu, 23 Sep 2004 00:06:28 +0200
Cc: Andrew Grover <andy.grover@xxxxxxxxx>, ak@xxxxxxx, anton@xxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <20040922133906.7d57ef49.davem@xxxxxxxxxxxxx>
References: <20040920063012.GL2825@krispykreme> <20040920203021.GD4242@xxxxxxxxxxxxx> <20040921155835.18aee381.davem@xxxxxxxxxxxxx> <20040922140000.GD27432@xxxxxxxxxxxxx> <20040922111209.7887df53.davem@xxxxxxxxxxxxx> <20040922195515.GA2619@xxxxxxxxxxxxx> <c0a09e5c04092213126ba5f29d@xxxxxxxxxxxxxx> <20040922133906.7d57ef49.davem@xxxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
> One thing that could be biting us is the nagle check which
> probably needs to be adjusted to use the standard MSS not
> the TSO one... perhaps play with this patch:

I tried it and it breaks the performance completely
(21MB/s) 

-Andi

> 
> ===== include/net/tcp.h 1.88 vs edited =====
> --- 1.88/include/net/tcp.h    2004-09-14 13:57:07 -07:00
> +++ edited/include/net/tcp.h  2004-09-22 13:18:43 -07:00
> @@ -1505,7 +1505,7 @@
>        * final FIN frame.  -DaveM
>        */
>       return (((nonagle&TCP_NAGLE_PUSH) || tp->urg_mode
> -              || !tcp_nagle_check(tp, skb, cur_mss, nonagle)) &&
> +              || !tcp_nagle_check(tp, skb, tp->mss_cache_std, nonagle)) &&
>               (((tcp_packets_in_flight(tp) + (pkts-1)) < tp->snd_cwnd) ||
>                (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)) &&
>               !after(TCP_SKB_CB(skb)->end_seq, tp->snd_una + tp->snd_wnd));
> 
> 

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