linux-kernel - Re: [PATCH 5/6] perf_counter: add more context information

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Date:	Thu, 02 Apr 2009 20:29:58 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] perf_counter: add more context information

On Thu, 2009-04-02 at 20:18 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > On Thu, 2009-04-02 at 13:36 +0200, Ingo Molnar wrote:
> > 
> > > > -#define MAX_STACK_DEPTH		255
> > > > +#define MAX_STACK_DEPTH		254
> > > >  
> > > >  struct perf_callchain_entry {
> > > > -	u64	nr;
> > > > +	u32	nr, hv, kernel, user;
> > > >  	u64	ip[MAX_STACK_DEPTH];
> > > >  };
> > 
> > Oh, and Paul suggested using u16s right after I send it out. So 
> > I'll either send an update or send a incremental in case you 
> > already applied it.
> 
> yes, that's probably a good idea. Although u8 might be even better - 
> do we ever want to do more than 256 deep stack vectors? Even those 
> would take quite some time to construct and pass down.

We'd have to pad it with 4 more bytes to remain u64 aligned, also, why
restrict ourselves. That MAX_STACK_DEPTH limit is trivially fixable if
indeed someone finds its insufficient.



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