linux-kernel - Re: Warning from ring buffer code (Was: Re: linux-next: tip tree build warning)

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Message-ID: <20090914184123.GC6045@nowhere>
Date:	Mon, 14 Sep 2009 20:41:24 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <srostedt@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Christopher Li <sparse@...isli.org>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org,
	Josh Triplett <josh@...edesktop.org>
Subject: Re: Warning from ring buffer code (Was: Re: linux-next: tip tree
	build warning)

On Mon, Sep 14, 2009 at 02:31:16PM -0400, Steven Rostedt wrote:
> On Mon, 2009-09-14 at 20:23 +0200, Peter Zijlstra wrote:
> > On Mon, 2009-09-14 at 14:17 -0400, Steven Rostedt wrote:
> > > Frederic, how big can one of those events get. The ring buffer (and
> > > TRACE_EVENT) allow up to almost a page size, which is very hefty for the
> > > stack. This code needs to either be rewritten or we need to set a limit
> > > to the size of a profile entry.
> > 
> > Yeah, that needs to get a re-write.. I've complained about this when it
> > went in.
> 
> One answer is to create a per cpu buffer that is big enough to hold the
> data needed. Then you can disable interrupts an use it without worry.
> 
> If you need to also handle NMIs, then create a per_cpu NMI buffer too,
> and use that if "in_nmi()" is true.
> 
> -- Steve


Looks like a nice idea.

Peter, does that sound acceptable to you to disable interrupts during a
profiled tracepoint event?

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