[fedora-arm] Fedora 20 for Raspberry Pi????

Richard W.M. Jones rjones at redhat.com
Fri Dec 27 16:02:36 UTC 2013

On Fri, Dec 27, 2013 at 09:53:54AM +0000, Gordan Bobic wrote:
> How is transparent alignment fixup going to give you back the
> performance you lose from accesses straddling cache lines?

You can have structs straddling cache lines and causing performance
problems without alignment issues, or structs being packed too close
together causing false sharing again w/o alignment being involved.

If alignment problems cause performance issues, then we should deal
with those performance problems.  If they don't, we shouldn't worry
about them.


ObHack: I once worked with an architecture [68k-based VME hardware]
that not only faulted on unaligned access, but also on accesses of the
wrong *size* (eg. using a short-sized read instruction instead of a
word-sized read instruction).  Dealing with that nonsense involved a
lot of compiler-specific massaging of code and some inline assembly ...

Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.

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