Messages in this thread | | | Date | Fri, 12 Sep 2003 11:11:48 -0700 | From | Tim Hockin <> | Subject | Re: Memory mapped IO vs Port IO |
| |
On Fri, Sep 12, 2003 at 08:00:03PM +0200, Andi Kleen wrote: > jbarnes@sgi.com (Jesse Barnes) writes: > > > Ok, Andi asked for benchmarks, so I ran some. Let this should be a > > lesson on why you shouldn't use port I/O :) I ran these on an SGI Altix > > w/900 MHz McKinley processors. > > > > Just straight calls to the routines (all of these are based on the > > average of 100 iterations): > > writeq(val, reg) time: 64 cycles > > outl(val, reg) time: 2126 cycles > ^^^^^ > > > > A simple branch: > > if (use_mmio) > > writeq(val, reg) time: 132 cycles > > else > > outl(val, reg) time: 1990 cycles > ^^^^^ > Something seems to be wrong in your numbers. > > Surely the outl in the if () cannot be faster than the pure outl() ?
Also - a perhaps more useful test is a write followed by a read.
-- Notice that as computers are becoming easier and easier to use, suddenly there's a big market for "Dummies" books. Cause and effect, or merely an ironic juxtaposition of unrelated facts?
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |