Subject: Re: more on cache ops... What are they actually supposed to do?
To: None <firstname.lastname@example.org>
From: Noriyuki Soda <email@example.com>
Date: 06/21/2000 04:56:49
mhitch> I've also alway thought there should be some cache invalidate
mhitch> operations for those cases where you don't need the cache
mhitch> flushed to memory.
cgd> yeah, the pre-DMA ops could use this type of thing, certainly.
jeffs> That's is a win too. The code has to be careful to avoid cache line
jeffs> tearing and invalidating outside the buffer. IRIX does this.
Yeah, not only invalidation, but also solely write-back operation is
desirable, since BUS_DMASYNC_PREWRITE of bus_dmamap_sync(9) may get
a benefit of it.
soren> Whoever does it should also keep Nisimura-san's recent suggestions
soren> in mind..
If I understand correctly, his proposal basically means having
following cache primitives:
- invalidate instruction cache
- invalidate data cache
- writeback and invalidate data cache
This is what our current FlushDCache() does.
On MIPS1, this should be just same function with
invalidation, since MIPS1's cache is write-through,
- writeback data cache
On MIPS1, this should be just no operation,
since MIPS1's cache is write-through,