On Tue, 18 Sep 2007, Luis R. Rodriguez wrote:
>
> An extra branch is created on MMIO-only devices on read/writes on the
> IO_COND macro using this interface -- or is this optimized out?
Umm. Does anybody actually have any performance numbers?
The thing is, those things are *cheap* compared to the IO. And any
high-performance device will be using DMA for the real IO, so we're not
generally even talking about any performance-critical stuff.
Quite frankly, if performance is a _real_ reason to avoid
ioread*/iowrite*, I'll happily accept read*/write*, but it would be needed
to be backed up by real numbers. Can you even measure it?
I would definitely *not* encourage the notion that people should use
readl/writel because of "performance reasons". That may be valid for some
fbcon driver, but those drivers go to other extremes (ie they use
"__raw_writel()" etc, and MTRR's etc).
If you don't use write-combining memory regions, the performance argument
is not really valid.
Linus
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