linux-kernel - Re: [RFC PATCH 4/6] ftrace: Allow stealing pages from pipe buffer

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Date:	Mon, 30 Jul 2012 18:12:21 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Amit Shah <amit.shah@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...64.org>,
	"Franch Ch. Eigler" <fche@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ingo Molnar <mingo@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	virtualization@...ts.linux-foundation.org, qemu-devel@...gnu.org,
	yrl.pp-manager.tt@...achi.com,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [RFC PATCH 4/6] ftrace: Allow stealing pages from pipe buffer

On Tue, 2012-07-24 at 11:37 +0900, Yoshihiro YUNOMAE wrote:
> From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> 
> Use generic steal operation on pipe buffer to allow stealing
> ring buffer's read page from pipe buffer.
> 
> Note that this could reduce the performance of splice on the
> splice_write side operation without affinity setting.
> Since the ring buffer's read pages are allocated on the
> tracing-node, but the splice user does not always execute
> splice write side operation on the same node. In this case,
> the page will be accessed from the another node.
> Thus, it is strongly recommended to assign the splicing
> thread to corresponding node.
> 
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve


> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> ---
> 
>  kernel/trace/trace.c |    8 +-------
>  1 files changed, 1 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a120f98..ae01930 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4194,12 +4194,6 @@ static void buffer_pipe_buf_release(struct pipe_inode_info *pipe,
>  	buf->private = 0;
>  }
>  
> -static int buffer_pipe_buf_steal(struct pipe_inode_info *pipe,
> -				 struct pipe_buffer *buf)
> -{
> -	return 1;
> -}
> -
>  static void buffer_pipe_buf_get(struct pipe_inode_info *pipe,
>  				struct pipe_buffer *buf)
>  {
> @@ -4215,7 +4209,7 @@ static const struct pipe_buf_operations buffer_pipe_buf_ops = {
>  	.unmap			= generic_pipe_buf_unmap,
>  	.confirm		= generic_pipe_buf_confirm,
>  	.release		= buffer_pipe_buf_release,
> -	.steal			= buffer_pipe_buf_steal,
> +	.steal			= generic_pipe_buf_steal,
>  	.get			= buffer_pipe_buf_get,
>  };
>  
> 


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