Messages in this thread | | | Subject | Re: [PATCH 1/2] perf: Correctly align perf event tracing buffer | From | Peter Zijlstra <> | Date | Mon, 29 Mar 2010 10:51:31 +0200 |
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On Sun, 2010-03-28 at 07:11 +0200, Frederic Weisbecker wrote: > The trace event buffer used by perf to record raw sample events > is typed as an array of char and may then not be aligned to 8 > by alloc_percpu(). > > But we need it to be aligned to 8 in sparc64 because we cast > this buffer into a random structure type built by the TRACE_EVENT() > macro to store the traces. So if a random 64 bits field is accessed > inside, it may be not under an expected good alignment. > > Use an array of long instead to force the appropriate alignment, and > perform a compile time check to ensure the size in byte of the buffer > is a multiple of sizeof(long) so that its actual size doesn't get > shrinked under us. > > This fixes unaligned accesses reported while using perf lock > in sparc 64. > > Suggested-by: David Miller <davem@davemloft.net> > Suggested-by: Tejun Heo <htejun@gmail.com> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Paul Mackerras <paulus@samba.org> > Cc: Ingo Molnar <mingo@elte.hu> > Cc: David Miller <davem@davemloft.net> > Cc: Steven Rostedt <rostedt@goodmis.org> > --- > 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?
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