cvs commit: src/sys/amd64/include _types.h src/sys/i386/include _types.h src/sys/net if_bridge.c src/sys/netinet ip_var.h src/sys/netinet6 ip6_var.h

[Peter Wemm]

On Monday 04 July 2005 02:40 am, Peter Grehan wrote:
> >   Check the alignment of the IP header before passing the packet up
> > to the packet filter. This would cause a panic on architectures
> > that require strict alignment such as sparc64 (tier1) and ia64/ppc
> > (tier2).
>
>   FYI, any modern ppc implementation doesn't require strict alignment
> for integer load/stores though there's a performance penalty for
> having to split the access into smaller ones.

As an aside, I've been contemplating taking a shot at having the AC 
(alignment checking) turned on for the amd64 kernel and see what 
breaks.  But rather than trying to do bit-shifting bcopys etc, I was 
thinking about toggling it off/on around known offenders.

It could be interesting to allow userland to turn it on/off for its own 
use as well.  But I suspect that touching %cr0 on the fly at syscall 
entry/exit could be a serious microcode cost.

But still, it might be an interesting thing to have available as a 
diagnostic tool.  Unaligned accesses are slower here too.  And there 
are ugly side effects if the unaligned access crosses a cache line 
boundary.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5