Messages in this thread | | | Date | Thu, 16 Jun 2011 14:32:41 +0100 | Subject | Re: [PATCH] ring_buffer: Ensure that buffer page data is aligned. | From | Will Newton <> |
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On Thu, Jun 16, 2011 at 2:17 PM, Steven Rostedt <rostedt@goodmis.org> wrote: > 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?
Yes, it's likely for all 64bit arches will be aligned correctly.
>> >> 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.
I have modified that conditional in my local tree so the patch is not a nop there. Obviously it doesn't make any sense to merge that change yet. I thought this part of the patch was a reasonable cleanup to make the code a bit more self documenting though. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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