On Wed, Jan 01, 2014 at 12:21:30PM -0800, Sean Omalley wrote: > They are a problem. It is a performance issue at the very least on > =ALL= platforms. There is a cost even on Intel's platform for > alignment errors, they just fix them up in hardware so it isn't as > big of a performance hit. It might be 5 cycles instead of 20. On Intel Sandybridge and up there is no penalty: http://www.agner.org/optimize/blog/read.php?i=142&v=t On earlier Intel processors it's not significant: http://lemire.me/blog/archives/2012/05/31/data-alignment-for-speed-myth-or-reality/ Anyway, you are optimizing far too early. If there's a performance problem, run 'perf', find out that it's caused by X where X might be the big misalignment penalty on ARM or many other things, then fix that. There's no need to go on a huge crusade to fix every last mis- alignment, because that will involve vast hours of programmer effort for no measurable gain. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org _______________________________________________ arm mailing list arm@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/arm
