> OK, currently we have CONFIG_AMD_K5_WTALLOC, CONFIG_AMD_K6_WTALLOC,
> CONFIG_AMD_K6_WTALLOC_WCDE and CONFIG_AMD_K6_WTALLOC_WAE15M in
> Configure.help. Anybody have any ideas when we'll be able to see some
> actual code which does that? Seems interesting :)
This is part of the non-Intel x86 stuff that went in to the CVS
tree (some know it as the Cyrix patch). This hasn't yet made it
to Linus' kernel although the config options have. Unlike many
of the new options the non-Intel stuff also includes entries
to Configure.help to tell you what's going on. If they aren't
there yet they will presumably arrive with the actual code.
The WTALLOC stuff enables allocation of cache lines on writes as
well as reads. This is a win when you copy something then use the
copy but a loss if you don't use the copy or only use a relatively
small part of it. I optioned it because it isn't clear if this
is a general case win or not. Typically you will lose when you
have to zero or copy a page (because the act of writing it will
allocate rather more L1 lines than you want) but more general
code (kernel and user) gains because programmers rarely do a
read before write to optimise cache allocation (and to do it
optimally requires that you know some detail about the cache
behaviour anyway). Swings 'n roundabouts stuff and I don't
consider my usage "general" :-).
The AMD options may not even work. I don't have an AMD and I
can't remember anyone ever mentioning whether it worked or not.
Mike
-- .----------------------------------------------------------------------. | Mike Jagdis | Internet: mailto:mike@roan.co.uk | | Roan Technology Ltd. | | | 54A Peach Street, Wokingham | Telephone: +44 118 989 0403 | | RG40 1XG, ENGLAND | Fax: +44 118 989 1195 | `----------------------------------------------------------------------'