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

[Frederic Weisbecker]

On Mon, Mar 29, 2010 at 07:20:09PM +0200, Peter Zijlstra wrote:
> On Mon, 2010-03-29 at 19:16 +0200, Frederic Weisbecker wrote:
> > 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.
> 
> Also, if you need u64 alignment, shouldn't you use u64 instead of
> unsigned long, the alignment requirement on those two might differ on
> 32bit machines.


Yeah but we need the u64 alignment only on 64 bits machines.

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