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

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Date:	Fri, 29 Jun 2012 15:17:19 -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 Fri, 2012-06-29 at 08:25 -0400, Steven Rostedt wrote:
> 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.

Can you make this change and repost the patch. I'll start testing it if
you can ASAP. Otherwise it will have to wait till next week.

-- Steve

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


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