linux-kernel - Re: [PATCH] tracing: Update entries counter when removing pages

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Date:	Fri, 29 Jun 2012 08:25:41 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
Cc:	Justin Teravest <teravest@...gle.com>,
	David Sharp <dhsharp@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Update entries counter when removing pages

On Mon, 2012-06-18 at 12:12 -0700, Vaibhav Nagarnaik wrote:
> When removing pages from the ring buffer, its state is not reset. This
> means that the counters need to be correctly updated to account for the
> pages removed.
> 
> Update the entries counter to reflect the removed events from the
> pages just like entries_bytes counter.
> 
> Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@...gle.com>
> ---
>  kernel/trace/ring_buffer.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 96c2dd1..a2bec4c 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1346,10 +1346,10 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
>  			 * If something was added to this page, it was full
>  			 * since it is not the tail page. So we deduct the
>  			 * bytes consumed in ring buffer from here.
> -			 * No need to update overruns, since this page is
> -			 * deleted from ring buffer and its entries are
> -			 * already accounted for.
> +			 * No need to update overruns, since updating
> +			 * 'entries' accounts for that.
>  			 */
> +			local_sub(page_entries, &cpu_buffer->entries);

Actually, I think it would be better to increment overrun instead. As
these are lost events, and that is what overrun counts. I just tested it
with: local_add(page_entries, &cpu_buffer->overrun); and it works well.
Showing the lost events.

-- Steve

>  			local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
>  		}
>  


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