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

Jens Axboe
2009-01-08T19:46:00Z

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@1wt.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@1wt.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