Messages in this thread | | | Date | Thu, 11 Sep 2003 18:31:36 +0200 | From | Andi Kleen <> | Subject | Re: Memory mapped IO vs Port IO |
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On Thu, 11 Sep 2003 17:25:04 +0100 Matthew Wilcox <willy@debian.org> wrote:
> On Thu, Sep 11, 2003 at 06:17:02PM +0200, Andi Kleen wrote: > > The overhead of checking for PIO vs mmio at runtime in the drivers > > should be completely in the noise on any non ancient CPU (both MMIO > > and PIO typically take hundreds or thousands of CPU cycles for the bus > > access, having an dynamic function call or an if before that is makes > > no difference at all) > > That's not true for MMIO writes which are posted. They should take > no longer than a memory write. For MMIO reads and PIO reads & writes, > you are, of course, correct.
Even a memory write is tens to hundres of cycles.
-Andi
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