2021-06-02 11:57:03

by Leo Yan

Subject: [PATCH v2 5/8] perf auxtrace: Change to use SMP memory barriers

The kernel and the userspace tool can access the AUX ring buffer head
and tail from different CPUs, thus SMP class of barriers are required
on SMP system.

This patch changes to use SMP barriers to replace mb() and rmb()
barriers.

Signed-off-by: Leo Yan <[email protected]>
---
tools/perf/util/auxtrace.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
index a4fbb33b7245..42b7ef811bde 100644
--- a/tools/perf/util/auxtrace.h
+++ b/tools/perf/util/auxtrace.h
@@ -444,7 +444,7 @@ static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm)
u64 head = READ_ONCE(pc->aux_head);

/* Ensure all reads are done after we read the head */
- rmb();
+ smp_rmb();
return head;
}

@@ -458,7 +458,7 @@ static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm)
#endif

/* Ensure all reads are done after we read the head */
- rmb();
+ smp_rmb();
return head;
}

@@ -470,7 +470,7 @@ static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail)
#endif

/* Ensure all reads are done before we write the tail out */
- mb();
+ smp_mb();
#if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT)
pc->aux_tail = tail;
#else
--
2.25.1

2021-06-07 10:06:01

by Adrian Hunter

Subject: Re: [PATCH v2 5/8] perf auxtrace: Change to use SMP memory barriers

On 2/06/21 1:30 pm, Leo Yan wrote:
> The kernel and the userspace tool can access the AUX ring buffer head
> and tail from different CPUs, thus SMP class of barriers are required
> on SMP system.
>
> This patch changes to use SMP barriers to replace mb() and rmb()
> barriers.
>
> Signed-off-by: Leo Yan <[email protected]>

Acked-by: Adrian Hunter <[email protected]>

> ---
> tools/perf/util/auxtrace.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
> index a4fbb33b7245..42b7ef811bde 100644
> --- a/tools/perf/util/auxtrace.h
> +++ b/tools/perf/util/auxtrace.h
> @@ -444,7 +444,7 @@ static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm)
> u64 head = READ_ONCE(pc->aux_head);
>
> /* Ensure all reads are done after we read the head */
> - rmb();
> + smp_rmb();
> return head;
> }
>
> @@ -458,7 +458,7 @@ static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm)
> #endif
>
> /* Ensure all reads are done after we read the head */
> - rmb();
> + smp_rmb();
> return head;
> }
>
> @@ -470,7 +470,7 @@ static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail)
> #endif
>
> /* Ensure all reads are done before we write the tail out */
> - mb();
> + smp_mb();
> #if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT)
> pc->aux_tail = tail;
> #else
>

2021-06-07 15:34:01

by Peter Zijlstra

Subject: Re: [PATCH v2 5/8] perf auxtrace: Change to use SMP memory barriers

On Wed, Jun 02, 2021 at 06:30:04PM +0800, Leo Yan wrote:
> The kernel and the userspace tool can access the AUX ring buffer head
> and tail from different CPUs, thus SMP class of barriers are required
> on SMP system.
>
> This patch changes to use SMP barriers to replace mb() and rmb()
> barriers.
>
> Signed-off-by: Leo Yan <[email protected]>

Acked-by: Peter Zijlstra (Intel) <[email protected]>

2021-06-09 06:20:40

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH v2 5/8] perf auxtrace: Change to use SMP memory barriers

Em Mon, Jun 07, 2021 at 05:29:55PM +0200, Peter Zijlstra escreveu:
> On Wed, Jun 02, 2021 at 06:30:04PM +0800, Leo Yan wrote:
> > The kernel and the userspace tool can access the AUX ring buffer head
> > and tail from different CPUs, thus SMP class of barriers are required
> > on SMP system.
> >
> > This patch changes to use SMP barriers to replace mb() and rmb()
> > barriers.
> >
> > Signed-off-by: Leo Yan <[email protected]>
>
> Acked-by: Peter Zijlstra (Intel) <[email protected]>

Thanks, applied.

- Arnaldo