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SubjectRe: [PATCH] x86: remove byte locks
On Tue, 13 Jan 2009, Jeremy Fitzhardinge wrote:

> My intention for that code was always that it be a simplest-possible
> reference implementation for the spinlock pvops, and perhaps a basis for
> a more specialized version (the Xen version is based on byte locks, for
> example). The code is "dead" in the sense that it has no users, but it
> also results in no generated code, and should be easy to maintain if the
> spinlock API is changed (as it is a canary to show that the other
> implementations will need changing too). In particular, the "paravirt
> spinlock" mechanism relies on all implementations using the same static
> initializer, and I wanted there to be an obvious second implementation
> so that if someone decided to change the ticketlock initializer, they'd
> be forced to consider what happens with the bytelock initializer (and by
> extension, any other implementation).

Why can't this just be somewhere in documentation? (possibly even with the
byte locks code as a reference).

It is IMHO just totally confusing to have a spinlock implementation that
is not used at all in the tree. It took me quite some time to go through
this until I finally figured out that this code is actually never used.
Currently, on first sight it might seem that byte locks are used whenever
CONFIG_PARAVIRT is set, which is not true.

And apparently even Linus got confused by this, which also tells us
something by itself, see [1].

[1] http://marc.info/?l=linux-kernel&m=123144211719754&w=2

--
Jiri Kosina
SUSE Labs


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