linux-kernel - Re: [PATCH 1/2] perf: Correctly align perf event tracing buffer

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Message-ID: <20100329171615.GA5101@nowhere>
Date:	Mon, 29 Mar 2010 19:16:18 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	David Miller <davem@...emloft.net>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 1/2] perf: Correctly align perf event tracing buffer

On Mon, Mar 29, 2010 at 10:51:31AM +0200, Peter Zijlstra wrote:
> On Sun, 2010-03-28 at 07:11 +0200, Frederic Weisbecker wrote:
> >  kernel/trace/trace_event_perf.c |   11 +++++++++--
> >  1 files changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> > index 0709e4f..69941f3 100644
> > --- a/kernel/trace/trace_event_perf.c
> > +++ b/kernel/trace/trace_event_perf.c
> > @@ -15,7 +15,12 @@ EXPORT_PER_CPU_SYMBOL_GPL(perf_trace_regs);
> >  static char *perf_trace_buf;
> >  static char *perf_trace_buf_nmi;
> >  
> > -typedef typeof(char [PERF_MAX_TRACE_SIZE]) perf_trace_t ;
> > +/*
> > + * Force it to be aligned to unsigned long to avoid misaligned accesses
> > + * suprises
> > + */
> > +typedef typeof(unsigned long [PERF_MAX_TRACE_SIZE / sizeof(unsigned long)])
> > +	perf_trace_t;
> >  
> 
> wouldn't __aligned(8) be simpler?


David and Tejun seemed to prefer to create the alignment on the
type level rather than using an align.

I'm personally fine either way.

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