linux-kernel - [RFC 2/2] ** do not apply this patch ** Just for illustration purposes

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Date:   Wed, 13 Nov 2019 11:33:27 -0500
From:   "Frank A. Cancio Bello" <frank@...eralsoftwareinc.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     joel@...lfernandes.org, saiprakash.ranjan@...eaurora.org
Subject: [RFC 2/2] ** do not apply this patch ** Just for illustration
 purposes

Prints a message that will allow us to evaluate the number of pages
allocated by each CPU buffer as well the main values that participate
in its calculation.

 $ echo 0 > /sys/kernel/debug/tracing/tracing_on
 $ echo 4096 > /sys/kernel/debug/tracing/buffer_size_kb
   .... e.g. of output:
   PAGE_SIZE: 4096, BUF_PAGE_HDR_SIZE: 16, size: 4194304, nr_pages: 1029

Signed-off-by: Frank A. Cancio Bello <frank@...eralsoftwareinc.com>
---
 kernel/trace/ring_buffer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 66358d66c933..c10b6bcb29b9 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1730,6 +1730,8 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 		return size;
 
 	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
+	printk(KERN_ALERT "PAGE_SIZE: %lu, BUF_PAGE_HDR_SIZE: %lu, size: %lu, nr_pages: %ld",
+	       PAGE_SIZE, BUF_PAGE_HDR_SIZE, size, nr_pages);
 
 	/* we need a minimum of two pages */
 	if (nr_pages < 2)
-- 
2.17.1