unaligned trap errors on alpha

[Steve Langasek]

On Thu, 14 Sep 2000 profmakx.fmp at gmx.de wrote:

> Hi all!1

> This is my first post to this list so please dont nuke me :-)

> Ive got a little problem with my alpha-smb-server under suse linux 6.4. I 
> downloaded the sources for samba to compile the newest version with 
> support for domain-logons ( for the win98 machines on my network ).
> The read performance is O.K, but when it comes to writing performance 
> drops ( no it isnt there anymore ). Whenever this happens, I get 
> "unaligned trap errors". I know that it is a programming issue as alpha 
> as other RISC CPUs can only access aligned data ... If additional 
> information is needed I can provide it.

This seems to be a frequent problem on Linux/Alpha, although I see fewer of
these as time goes on.  If you're seeing a lot of unaligned traps, that will
definitely cause a performance drop because every one of those traps
represents an instruction that has to be cleaned up by the kernel before it
can be handed to the processor -- definitely an expensive operation.

Unaligned traps tend to be easy to fix, but hard to pinpoint.  I'm sure that
any information you could provide to make it easier to pinpoint would be
useful.

BTW, what version of Samba does SuSE 6.4 ship with? It's also possible that
this problem has already been fixed, and that you can improve performance just
by upgrading to Samba 2.0.7.

Steve Langasek
postmodern programmer