linux-kernel - Re: [PATCH] tcp: splice as many packets as possible at once

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Message-ID: <20090108194424.GE32491@kernel.dk>
Date:	Thu, 8 Jan 2009 20:44:24 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Willy Tarreau <w@....eu>
Cc:	David Miller <davem@...emloft.net>,
	Jarek Poplawski <jarkao2@...il.com>,
	Ben Mansell <ben@...s.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: splice as many packets as possible at once

On Thu, Jan 08 2009, Willy Tarreau wrote:
> Jens,
> 
> here's the other patch I was talking about, for better behaviour of
> non-blocking splice(). Ben Mansell also confirms similar improvements
> in his tests, where non-blocking splice() initially showed half of
> read()/write() performance. Ben, would you mind adding a Tested-By
> line ?

Looks very good to me, I don't see any valid reason to have that !timeo
break. So feel free to add my acked-by to that patch and send it to
Dave.

> 
> Also, please note that this is unrelated to the corruption bug I reported
> and does not fix it.
> 
> Regards,
> Willy
> 
> From fafe76713523c8e9767805cfdc7b73323d7bf180 Mon Sep 17 00:00:00 2001
> From: Willy Tarreau <w@....eu>
> Date: Thu, 8 Jan 2009 17:10:13 +0100
> Subject: [PATCH] tcp: splice as many packets as possible at once
> 
> Currently, in non-blocking mode, tcp_splice_read() returns after
> splicing one segment regardless of the len argument. This results
> in low performance and very high overhead due to syscall rate when
> splicing from interfaces which do not support LRO.
> 
> The fix simply consists in not breaking out of the loop after the
> first read. That way, we can read up to the size requested by the
> caller and still return when there is no data left.
> 
> Performance has significantly improved with this fix, with the
> number of calls to splice() divided by about 20, and CPU usage
> dropped from 100% to 75%.
> 
> Signed-off-by: Willy Tarreau <w@....eu>
> ---
>  net/ipv4/tcp.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 35bcddf..80261b4 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -615,7 +615,7 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
>  		lock_sock(sk);
>  
>  		if (sk->sk_err || sk->sk_state == TCP_CLOSE ||
> -		    (sk->sk_shutdown & RCV_SHUTDOWN) || !timeo ||
> +		    (sk->sk_shutdown & RCV_SHUTDOWN) ||
>  		    signal_pending(current))
>  			break;
>  	}
> -- 
> 1.6.0.3
> 

-- 
Jens Axboe

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