dm writecache: improve performance on DDR persistent memory (Optane)

	return r;

}

static void memcpy_flushcache_optimized(void *dest, void *source, size_t size)

{

	/*

	 * clflushopt performs better with block size 1024, 2048, 4096

	 * non-temporal stores perform better with block size 512

	 *

	 * block size   512             1024            2048            4096

	 * movnti       496 MB/s        642 MB/s        725 MB/s        744 MB/s

	 * clflushopt   373 MB/s        688 MB/s        1.1 GB/s        1.2 GB/s

	 *

	 * We see that movnti performs better for 512-byte blocks, and

	 * clflushopt performs better for 1024-byte and larger blocks. So, we

	 * prefer clflushopt for sizes >= 768.

	 *

	 * NOTE: this happens to be the case now (with dm-writecache's single

	 * threaded model) but re-evaluate this once memcpy_flushcache() is

	 * enabled to use movdir64b which might invalidate this performance

	 * advantage seen with cache-allocating-writes plus flushing.

	 */

#ifdef CONFIG_X86

	if (static_cpu_has(X86_FEATURE_CLFLUSHOPT) &&

	    likely(boot_cpu_data.x86_clflush_size == 64) &&

	    likely(size >= 768)) {

		do {

			memcpy((void *)dest, (void *)source, 64);

			clflushopt((void *)dest);

			dest += 64;

			source += 64;

			size -= 64;

		} while (size >= 64);

		return;

	}

#endif

	memcpy_flushcache(dest, source, size);

}

static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data)

{

	void *buf;

			}

		} else {

			flush_dcache_page(bio_page(bio));

			memcpy_flushcache(data, buf, size);

			memcpy_flushcache_optimized(data, buf, size);

		}

		bvec_kunmap_irq(buf, &flags);