From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Paul Mackerras <paulus@samba.org>,
David Miller <davem@davemloft.net>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 1/2] perf: Correctly align perf event tracing buffer
Date: Mon, 29 Mar 2010 10:51:31 +0200 [thread overview]
Message-ID: <1269852691.12097.162.camel@laptop> (raw)
In-Reply-To: <1269753066-17246-2-git-send-regression-fweisbec@gmail.com>
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?
next prev parent reply other threads:[~2010-03-29 9:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-28 5:11 [GIT PULL] perf fixes Frederic Weisbecker
2010-03-28 5:11 ` [PATCH 1/2] perf: Correctly align perf event tracing buffer Frederic Weisbecker
2010-03-29 8:51 ` Peter Zijlstra [this message]
2010-03-29 17:16 ` Frederic Weisbecker
2010-03-29 17:20 ` Peter Zijlstra
2010-03-29 17:51 ` Frederic Weisbecker
2010-03-28 5:11 ` [PATCH 2/2] perf: Use hot regs with software sched switch/migrate events Frederic Weisbecker
2010-03-29 8:49 ` Peter Zijlstra
2010-03-29 17:47 ` Frederic Weisbecker
2010-03-29 18:05 ` Peter Zijlstra
2010-03-29 22:43 ` Frederic Weisbecker
2010-03-29 22:53 ` Frederic Weisbecker
2010-03-30 18:54 ` Peter Zijlstra
2010-03-30 19:14 ` Frederic Weisbecker
2010-03-29 3:33 ` [GIT PULL] perf fixes Ingo Molnar
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