From: Christoph Hellwig > Sent: 04 May 2020 17:03 > > On Sun, May 03, 2020 at 09:20:19PM +0100, Chris Wilson wrote: > > > Err, why does i915 implements its own uncached memcpy instead of relying > > > on core functionality to start with? > > > > What is this core functionality that provides movntqda? > > A sensible name might be memcpy_uncached or mempcy_nontemporal. > But the important point is that this should be arch code with a common > fallback rather than hacking it up in drivers. More the point, you are trying to do a copy where: 1) The kernel isn't expected to read the data - so can bypass the cache. and maybe: 2) The data needs flushing from the cache to actual memory. and maybe: 3) The cache lines need invalidating. The fallbacks depend on the required behaviour. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
