On Tue, Jan 09, 2001 at 05:48:11PM -0800, Justin Carlson wrote: > Looking at the existing clear_page implementations for r4xx0, rm7k, and mips32 > in the mips/ tree, I see everyone issuing cache op 0xd for the address range of > the page being cleared. > > I'm wondering what the purpose is of these cache flushes...given a physically > tagged dcache, my understanding of the semantics of clear_page are that it just > zeros the page, in which case the cache ops are pointless overhead. > > Especially in the mips32 case, which uses cache op 0xd, which is undefined > implementation dependent according to my mips32 spec. The idea is to avoid unnecessary memory reads - all the read data would be overwritten anyway. The last time I benchmarked this routine on some machine it made a difference of about 4000 vs. 2500 c0_count cycles. I think that was on a R4600 RM200. Ralf
