Messages in this thread Patch in this message | | | Subject | Re: [PATCH] ring_buffer: Ensure that buffer page data is aligned. | From | Steven Rostedt <> | Date | Thu, 16 Jun 2011 09:17:19 -0400 |
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On Thu, 2011-06-16 at 14:03 +0100, Will Newton wrote: > Explicitly align the start of the buffer page data array to the > required arch alignment. This is required for architectures that > require 8 byte alignment but do not have a 8 byte local_t.
What arch does that? A 32bit arch that forces 8 byte alignment?
> > Signed-off-by: Will Newton <will.newton@imgtec.com> > --- > kernel/trace/ring_buffer.c | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > I don't believe that any currently in-tree architecture is affected by > this, but it can be an issue on 32bit architectures that require an > 8 byte aligment but only have a 32bit local_t. I think it's potentially > cleaner to make the alignment explicit anyway. > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 0ef7b4b..36d5699 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -215,6 +215,8 @@ EXPORT_SYMBOL_GPL(tracing_is_on); > # define RB_ARCH_ALIGNMENT 8U > #endif > > +#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT) > +
Note, the code above this is:
#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array)) #define RB_ALIGNMENT 4U #define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX) #define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) # define RB_FORCE_8BYTE_ALIGNMENT 0 # define RB_ARCH_ALIGNMENT RB_ALIGNMENT #else # define RB_FORCE_8BYTE_ALIGNMENT 1 # define RB_ARCH_ALIGNMENT 8U #endif
Which means that when CONFIG_64BIT is not set, RB_ARCH_ALIGNMENT is 4. This means that this patch is really a nop and doesn't do anything for your arch.
-- Steve
> /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */ > #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX > > @@ -363,7 +365,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data); > struct buffer_data_page { > u64 time_stamp; /* page time stamp */ > local_t commit; /* write committed index */ > - unsigned char data[]; /* data of buffer page */ > + unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */ > }; > > /*
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