The x86 memcpy_nontemporal() helper maps to memcpy_flushcache(), and the ZONE_DEVICE template-copy path uses it to copy one struct page at a time.
The relevant copy size is sizeof(struct page). On x86_64, the base struct page layout is 64 bytes. Adding either the KMSAN metadata pointers or an out-of-flags last_cpupid field can make it 80 bytes after alignment, and enabling both can make it 96 bytes. memcpy_flushcache() currently only has inline fixed-size cases for 4, 8, and 16 bytes. As a result, these constant-sized struct page copies fall through to __memcpy_flushcache() even though the compiler knows the copy size at the call site. Add fixed-size MOVNTI cases up to 96 bytes so the ZONE_DEVICE template-copy path can keep these struct page copies in the inline memcpy_flushcache() path. This matters for ZONE_DEVICE memmap initialization because the copy happens once per initialized struct page. For a 100 GB fsdax namespace with map=dev, this is about 25 million struct page copies during nd_pmem binding or rebinding. Tested in a VM with a 100 GB fsdax namespace device configured with map=dev and a 100 GB devdax namespace (align=2097152) on Intel Ice Lake server. Test procedure: Rebind the nd_pmem and dax_pmem drivers 30 times and collect the memmap initialization time from the pr_debug() output of memmap_init_zone_device(). With memcpy_nontemporal() used by the ZONE_DEVICE template-copy path: Average of rebinds for nd_pmem driver: 150.83 ms Average of rebinds for dax_pmem driver: 153.55 ms With this x86 fixed-size fastpath patch applied: Average of rebinds for nd_pmem driver: 96.79 ms Average of rebinds for dax_pmem driver: 119.04 ms This further reduces the average memmap initialization time measured during rebind by about 35.8% for nd_pmem and 22.5% for dax_pmem. Suggested-by: Borislav Petkov <[email protected]> Signed-off-by: Li Zhe <[email protected]> --- arch/x86/include/asm/string_64.h | 71 +++++++++++++++++++++++++------- 1 file changed, 56 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h index 21ae515ae35a..831d3dda3b38 100644 --- a/arch/x86/include/asm/string_64.h +++ b/arch/x86/include/asm/string_64.h @@ -82,23 +82,64 @@ int strcmp(const char *cs, const char *ct); #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE #define __HAVE_ARCH_MEMCPY_FLUSHCACHE 1 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) + +static __always_inline void movnti_4(void *dst, const void *src) +{ + asm volatile("movntil %1, %0" + : "=m"(*(u32 *)dst) + : "r"(*(const u32 *)src) + : "memory"); +} + +static __always_inline void movnti_8(void *dst, const void *src) +{ + asm volatile("movntiq %1, %0" + : "=m"(*(u64 *)dst) + : "r"(*(const u64 *)src) + : "memory"); +} + +static __always_inline void movnti_16(void *dst, const void *src) +{ + movnti_8(dst, src); + movnti_8(dst + 8, src + 8); +} + +static __always_inline void movnti_32(void *dst, const void *src) +{ + movnti_16(dst, src); + movnti_16(dst + 16, src + 16); +} + +static __always_inline void movnti_64(void *dst, const void *src) +{ + movnti_32(dst, src); + movnti_32(dst + 32, src + 32); +} + +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; - } + if (!__builtin_constant_p(cnt)) + return __memcpy_flushcache(dst, src, cnt); + + /* + * The relevant fixed-size copies here are the x86_64 struct page sizes: + * 64, 80, and 96 bytes. Keep 32-byte and 48-byte copies inline as well + * instead of sending those nearby fixed-size cases back to + * __memcpy_flushcache(). + */ + switch (cnt) { + case 4: movnti_4(dst, src); break; + case 8: movnti_8(dst, src); break; + case 16: movnti_16(dst, src); break; + case 32: movnti_32(dst, src); break; + case 48: movnti_32(dst, src); movnti_16(dst + 32, src + 32); break; + case 64: movnti_64(dst, src); break; + case 80: movnti_64(dst, src); movnti_16(dst + 64, src + 64); break; + case 96: movnti_64(dst, src); movnti_32(dst + 64, src + 64); break; + default: __memcpy_flushcache(dst, src, cnt); break; } - __memcpy_flushcache(dst, src, cnt); } #define memcpy_nontemporal memcpy_nontemporal -- 2.20.1
