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| author | Mikulas Patocka <mpatocka@redhat.com> | 2018-08-08 17:22:16 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-09-10 15:17:12 +0200 |
| commit | 02101c45ec5b19d607af7372680f5259050b4e9c (patch) | |
| tree | d2b817c7d7490aa655d9a3c4a8193c5c47fd60ad /arch/x86/include/asm/string_64.h | |
| parent | 11da3a7f84f19c26da6f86af878298694ede0804 (diff) | |
| download | lwn-02101c45ec5b19d607af7372680f5259050b4e9c.tar.gz lwn-02101c45ec5b19d607af7372680f5259050b4e9c.zip | |
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>
Diffstat (limited to 'arch/x86/include/asm/string_64.h')
| -rw-r--r-- | arch/x86/include/asm/string_64.h | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h index d33f92b9fa22..7ad41bfcc16c 100644 --- a/arch/x86/include/asm/string_64.h +++ b/arch/x86/include/asm/string_64.h @@ -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__ */ |