Re: Mmap device performance

Alan Cox (
Thu, 11 Dec 1997 18:12:18 +0000 (GMT)

> > the degradation must be happening somewhere in the kernel layers. I'm
> > currently mapping the region shared with read/write access.
> Oh, it also looks like mmap from /dev/mem disables caching. That's
> gotta hurt...

PCI memory access is uncached - it is meant to be, but for the P6 theres
a sort of "vaguely cached writes" mode called write-gathering that generates
burst writes.