On Mon, Jun 18 2018 at 8:50am -0400, Mikulas Patocka <[email protected]> wrote:
> Hi Mike > > Could you please push this patch to the kernel 4.18-rc? Dan Williams said > that he will submit it, but he forgot about it. > > Without this patch, dm-writecache is suffering 2% penalty because of > memcpy_flushcache overhead. I cannot send this to Linus directly, it needs to go through the x86 tree. I already tried to get a slightly revised version of this upstream, see: https://www.redhat.com/archives/dm-devel/2018-May/msg00080.html I'll try a resend.. but the 4.18 merge window is now closed. Mike > From: Mikulas Patocka <[email protected]> > > I use memcpy_flushcache in my persistent memory driver for metadata > updates and it turns out that the overhead of memcpy_flushcache causes 2% > performance degradation compared to "movnti" instruction explicitly coded > using inline assembler. > > 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 <[email protected]> > > --- > arch/x86/include/asm/string_64.h | 20 +++++++++++++++++++- > arch/x86/lib/usercopy_64.c | 4 ++-- > 2 files changed, 21 insertions(+), 3 deletions(-) > > Index: linux-2.6/arch/x86/include/asm/string_64.h > =================================================================== > --- linux-2.6.orig/arch/x86/include/asm/string_64.h > +++ linux-2.6/arch/x86/include/asm/string_64.h > @@ -149,7 +149,25 @@ memcpy_mcsafe(void *dst, const void *src > > #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__ */ > Index: linux-2.6/arch/x86/lib/usercopy_64.c > =================================================================== > --- linux-2.6.orig/arch/x86/lib/usercopy_64.c > +++ linux-2.6/arch/x86/lib/usercopy_64.c > @@ -153,7 +153,7 @@ long __copy_user_flushcache(void *dst, c > 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 > 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) _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
