netdev - Re: Splice status

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Message-ID: <AANLkTi=cTV69OnJ8-c064nA-F1xaV11KixviuvNMPFrR@mail.gmail.com>
Date:	Mon, 26 Jul 2010 15:41:25 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Ofer Heifetz <oferh@...vell.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Jens Axboe <axboe@...nel.dk>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: Splice status

On Sun, Jul 25, 2010 at 10:47 PM, Ofer Heifetz <oferh@...vell.com> wrote:
> Hi Eric,
>
> Still trying to get better performance with splice, I noticed that when using splice there are twice the file size memcpy (placed a counter in memcpy), I verified it via samba file transfer and splice-fromnet/out.
>
> I also used the splice-fromnet/out and using ftrace I did notice that data is copied twice using these routines: skb_splice_bits, pipe_to_file.
>
> I thought that the main goal of splice is to refrain from one copy when moving data from network to file descriptor.
>
> If there are the same number of memcpy and context switches and in samba copy additional vfs overhead it makes sense that splice deteriates the samba overall write performance.
>

The support for SPLICE_F_MOVE is removed by Nick in commit
http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commitdiff;h=485ddb4b9741bafb70b22e5c1f9b4f37dc3e85bd
.

Nick, can we add it back now?

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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