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x86/asm: Optimize memcpy_flushcache() 

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>
This commit is contained in:
Mikulas Patocka 2018-08-08 17:22:16 -04:00 committed by Ingo Molnar
parent 11da3a7f84
commit 02101c45ec
2 changed files with 21 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
arch/x86/include/asm/string_64.h
View File

@ -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__ */

4
arch/x86/lib/usercopy_64.c
View File

@ -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)