Hi,

I recently benchmarked the hardware memory subsystem of our MIPS-based
board (currently using PMC RM5231), and I was surprised to see that
memory writes were slower than memory reads. My benchmark routine uses
KSEG0 with write back for its tests.

So I took my books and found the reason quickly: in my case, memory
writes in a particular cacheline are preceded by a cache refill if the
line was previously unused. But in my case, these cache refill are not
needed since I write entire cachelines (I transfert large blocks of data
and measure the time it takes).

RM5231's datasheet states that this behaviour can be corrected by
issuing a "create dirty exclusive" cache operation on the lines
concerned. Doing so effectively increased write throughput: I can write
to memory at 125MBytes/s instead of 50MBytes/s.

So here comes my question/reflexion: could these modifications be
applied to NetBSD kernel, for example through memset/memcpy routines ?

--
Nicolas BOUQUET
Low-level software and hardware engineer
IPricot SA FRANCE