On Sat, May 25, 2002 at 01:18:06PM -0700, William Jhun wrote:
When preparing a buffer for a DMA transfer, we've found it's more
optimal to only do a wback_inv if the direction is not known
(PCIDMA_BIDIRECTIONAL), only a wback if transfer is to the device
(PCIDMA_TO_DEVICE), and only an invalidate if from the device
(PCIDMA_FROM_DEVICE). Such a modification has made a small (yet
significant) improvement for one of our network drivers during a packet
forwarding rate test.
*sigh*. On the platform we were testing on, we used our own cache code
(rm7k with tertiary cache support) which has been well-tested for over a
year now. In these routines, we implement dma_cache_wback and only do
invalidates (no flush) for dma_cache_wback_inv. Now that I'm looking
around in cache support for other MIPS CPUs, I see that all the _wback
calls are not implemented and that many (or all?) of the _inv calls also
flush the caches.
The patch below leaves the existing funtions alone and just adds the two
My question is: why are these dma_cache_wback calls not implemented? And
how come dma_cache_inv is treated the same as dma_cache_wback_inv? Are
we doing something wrong by implementing these calls in our cache code
as they are described?