[dm-devel] [PATCH 2/2] dm-writecache

[Mikulas Patocka]

On Thu, 23 Nov 2017, Dan Williams wrote:

> On Thu, Nov 23, 2017 at 12:29 AM, Christoph Hellwig <hch at infradead.org> wrote:
> >> +/*
> >> + * The clflushopt instruction is very slow on Broadwell, so we use non-temporal
> >> + * stores instead.
> >> + */
> >> +#ifdef CONFIG_X86_64
> >> +#define NT_STORE(dest, src)  asm ("movnti %1, %0" : "=m"(dest) : "r"(src))
> >> +#define FLUSH_RANGE(dax, ptr, size)  do { } while (0)
> >> +#define COMMIT_FLUSHED()     wmb()
> >> +#else
> >> +#define NT_STORE(dest, src)  ACCESS_ONCE(dest) = (src)
> >> +#define FLUSH_RANGE          dax_flush
> >> +#define COMMIT_FLUSHED()     do { } while (0)
> >> +#endif
> >
> > Please go through the proper pmem APIs.
> 
> Yes, see _copy_from_iter_flushcache() and all its related apis.
> Drivers shouldn't be doing anything different than what fs/dax.c is
> using.

There is not any arch-independent API that abstracts over a single movnti 
instruction.

Do you want to add it?

memcpy_flushcache is overkill for one or two 8-byte stores. And - on 
non-x86 architectures memcpy_flushcache doesn't flush cache at all.

Mikulas