On Sat, 25 Jun 2016 01:15:34 +0900
Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> On Fri, Jun 24, 2016 at 12:04:40PM -0400, Steven Rostedt wrote:
> > On Fri, 24 Jun 2016 15:35:44 +0900
> > Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> >
> >
> > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > > > > index dea12a6e413b..35c523ba5c59 100644
> > > > > --- a/include/linux/ftrace.h
> > > > > +++ b/include/linux/ftrace.h
> > > > > @@ -751,25 +751,33 @@ extern void ftrace_init(void);
> > > > > static inline void ftrace_init(void) { }
> > > > > #endif
> > > > >
> > > > > +#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
> > > > > +# define FTRACE_ALIGNMENT 4
> > > > > +#else
> > > > > +# define FTRACE_ALIGNMENT 8
> > > > > +#endif
> > > >
>
> As far as I can see, the ring buffer has following code in ring_buffer.c:
>
> #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 */
>
> #ifndef CONFIG_HAVE_64BIT_ALIGNED_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
>
> #define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
>
Right, what I meant was that we should just define FTRACE_ALIGNMENT
unconditionally to 4. If CONFIG_HAVE_64BIT_ALIGNED_ACCESS is not set,
it will add the buffered space regardless.
You already moved "overrun", I don't see anything that would be out of
alignment if the structure itself is aligned.
-- Steve
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