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

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Message-ID: <c62985530909150201p3d5ca037g232c9456e6436fc@mail.gmail.com>
Date:	Tue, 15 Sep 2009 11:01:15 +0200
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <srostedt@...hat.com>,
	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)

2009/9/15, Peter Zijlstra <peterz@...radead.org>:
> On Mon, 2009-09-14 at 20:41 +0200, Frederic Weisbecker wrote:
>> 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?
>
> It does anyway, a little further down the line, so sure.


Ok I'll fix it soon using Steve's idea then.

Thanks.
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