x86/asm: Optimize memcpy_flushcache() (02101c45) · Commits · 戴 / test

I use memcpy_flushcache() in my persistent memory driver for metadata updates, there are many 8-byte and 16-byte updates and it turns out that the overhead of memcpy_flushcache causes 2% performance degradation compared to "movnti" instruction explicitly coded using inline assembler. The tests were done on a Skylake processor with persistent memory emulated using the "memmap" kernel parameter. dd was used to copy data to the dm-writecache target. This patch recognizes memcpy_flushcache calls with constant short length and turns them into inline assembler - so that I don't have to use inline assembler in the driver. Signed-off-by:

Mikulas Patocka <mpatocka@redhat.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Snitzer <snitzer@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: device-mapper development <dm-devel@redhat.com> Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1808081720460.24747@file01.intranet.prod.int.rdu2.redhat.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/string_64.h

+19 −1

Original line number	Diff line number	Diff line
		@@ -149,7 +149,25 @@ memcpy_mcsafe(void dst, const void src, size_t cnt)

		#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
		#define __HAVE_ARCH_MEMCPY_FLUSHCACHE 1
		void memcpy_flushcache(void dst, const void src, size_t cnt);
		void __memcpy_flushcache(void dst, const void src, size_t cnt);
		static __always_inline void memcpy_flushcache(void dst, const void src, size_t cnt)
		{
		if (__builtin_constant_p(cnt)) {
		switch (cnt) {
		case 4:
		asm ("movntil %1, %0" : "=m"((u32 )dst) : "r"((u32 )src));
		return;
		case 8:
		asm ("movntiq %1, %0" : "=m"((u64 )dst) : "r"((u64 )src));
		return;
		case 16:
		asm ("movntiq %1, %0" : "=m"((u64 )dst) : "r"((u64 )src));
		asm ("movntiq %1, %0" : "=m"((u64 )(dst + 8)) : "r"((u64 )(src + 8)));
		return;
		}
		}
		__memcpy_flushcache(dst, src, cnt);
		}
		#endif

		#endif /* __KERNEL__ */

arch/x86/lib/usercopy_64.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -153,7 +153,7 @@ long __copy_user_flushcache(void dst, const void __user src, unsigned size)
		return rc;
		}

		void memcpy_flushcache(void _dst, const void _src, size_t size)
		void __memcpy_flushcache(void _dst, const void _src, size_t size)
		{
		unsigned long dest = (unsigned long) _dst;
		unsigned long source = (unsigned long) _src;
		@@ -216,7 +216,7 @@ void memcpy_flushcache(void _dst, const void _src, size_t size)
		clean_cache_range((void *) dest, size);
		}
		}
		EXPORT_SYMBOL_GPL(memcpy_flushcache);
		EXPORT_SYMBOL_GPL(__memcpy_flushcache);

		void memcpy_page_flushcache(char to, struct page page, size_t offset,
		size_t len)

Admin message