linux-kernel - Re: [PATCH v3] ring-buffer/Documentation: Add documentation on buffer

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Message-ID: <4ad2944b-db65-4877-b388-2bcaa23e88ec@infradead.org>
Date: Sat, 30 Dec 2023 20:39:16 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>, LKML
 <linux-kernel@...r.kernel.org>,
 Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
 linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v3] ring-buffer/Documentation: Add documentation on
 buffer_percent file



On 12/29/23 09:24, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> When the buffer_percent file was added to the kernel, the documentation
> should have been updated to document what that file does.
> 
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Fixes: 03329f9939781 ("tracing: Add tracefs file buffer_percentage")
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

LGTM. Thanks.
Acked-by: Randy Dunlap <rdunlap@...radead.org>

> ---
> Changes since v2: https://lore.kernel.org/linux-trace-kernel/20231226130149.4685c838@gandalf.local.home
> 
> - s/watermark/water-mark/ (Randy Dunlap)

That comment is backwards. :)
No new patch needed IMO.

> 
> - Added '::' and indented the number list so that it has better
>   formatting (kernel test robot)
> 
>  Documentation/trace/ftrace.rst | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
> index 933e7efb9f1b..917501a2f348 100644
> --- a/Documentation/trace/ftrace.rst
> +++ b/Documentation/trace/ftrace.rst
> @@ -180,6 +180,21 @@ of ftrace. Here is a list of some of the key files:
>  	Only active when the file contains a number greater than 0.
>  	(in microseconds)
>  
> +  buffer_percent:
> +
> +	This is the watermark for how much the ring buffer needs to be filled
> +	before a waiter is woken up. That is, if an application calls a
> +	blocking read syscall on one of the per_cpu trace_pipe_raw files, it
> +	will block until the given amount of data specified by buffer_percent
> +	is in the ring buffer before it wakes the reader up. This also
> +	controls how the splice system calls are blocked on this file::
> +
> +	  0   - means to wake up as soon as there is any data in the ring buffer.
> +	  50  - means to wake up when roughly half of the ring buffer sub-buffers
> +	        are full.
> +	  100 - means to block until the ring buffer is totally full and is
> +	        about to start overwriting the older data.
> +
>    buffer_size_kb:
>  
>  	This sets or displays the number of kilobytes each CPU

-- 
#Randy