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SubjectRe: [PATCH] add new DMA_ADDR_T_SIZE define
On 19 Feb 2003, James Bottomley wrote:

> > 3. use run-time checks all over the place, of the
> > "sizeof(dma_addr_t)==sizeof(u64)" kind, which adds unnecessary
> > overhead to
> > all platforms.
> Actually, these aren't technically run time checks. Although the cpp
> can't be used for sizeof(), the compiler (at least gcc) does seem to
> have enough sense to optimise away if(..) branches it has enough
> information to know won't be taken at compile time.
> As long as this optimisation works, I think the if(sizeof(..)) checks
> are fine for this.

Well, yes and no. Indeed those checks are optimized away, but as a result
of using them most data-access macros must be converted to inline
functions. And, last I heard at least, gcc was optimizing inline functions
much worse than preprocessor macros.

There are various other things that are made easier by a preprocessor
directive -- constructing the right data structures, for instance.

However, if such a patch is ultimately not getting accepted, these checks
is probably what I'll end up using...


It is better to keep your mouth shut and be thought a fool,
than to open it and remove all doubt.

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