Re: [RFC 1/2] ftrace porting of ia64

[Ingo Molnar <mingo@elte.hu>]

* Steven Rostedt <srostedt@redhat.com> wrote:

> 
> On Thu, 2008-12-18 at 11:25 +0100, Ingo Molnar wrote:
> > * Shaohua Li <shaohua.li@intel.com> wrote:
> > 
> > > ftrace porting of IA64.
> > > TBD:
> > > 1. I don't how to add unwind info to the assemble code, so please
> > > advise.
> > > 2. The generic ftrace ring buffer code doesn't handle alignment well.
> > > With the patch, kernel will report a lot of unalignment. This is still
> > > under investigation.
> > 
> > hm, that's weird - i recently profiled 64-bit x86 for unaligned accesses 
> > and there didnt seem to be many. In any case, feel free to fix any 
> > unaligned structure fields by reordering them.
> 
> Will x86_64 break if something is aligned by 32 bits?

No, but there are tools to detect misalignment as they happen. (there are 
CPU hw counters for access misalignment and kerneltop can profile based on 
that info :-)

> The records in the buffer use to be 64 bit aligned. They are now 32 bit 
> aligned. I wonder if we should make that alignment arch specific.

No, we should just align them to 64 bits and be done with it.

	Ingo