| Message ID | alpine.LRH.2.02.1806180846300.22626@file01.intranet.prod.int.rdu2.redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Jun 18 2018 at 8:50am -0400, Mikulas Patocka <mpatocka@redhat.com> 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 <mpatocka@redhat.com> > > 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 <mpatocka@redhat.com> > > --- > 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)
On Mon, Jun 18, 2018 at 5:50 AM, Mikulas Patocka <mpatocka@redhat.com> 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. ...to be clear I acked it and asked Ingo to take it. Will need a resubmit for 4.19. Ingo, see below for a patch to pick up into -tip when you have a chance. > > Without this patch, dm-writecache is suffering 2% penalty because of > memcpy_flushcache overhead. > > Mikulas > > > > From: Mikulas Patocka <mpatocka@redhat.com> > > 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 <mpatocka@redhat.com> > > --- > 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)
Hi, I'm a bit late on this but I have a question about the original patch - I thought that in order for movnt (movntil, movntiq) to push the data into the persistency domain (ADR), one must work with length that is multiple of cacheline size, otherwise the write-combine buffers remain partially filled and you need to commit them with a fence (sfence) - which ruins the whole performance gain you got here. Am I wrong, are the write-combine buffers are part of the ADR domain or something? Thanks, Yigal On Mon, Jun 18, 2018 at 7:38 PM, Dan Williams <dan.j.williams@intel.com> wrote: > On Mon, Jun 18, 2018 at 5:50 AM, Mikulas Patocka <mpatocka@redhat.com> 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. > > ...to be clear I acked it and asked Ingo to take it. Will need a > resubmit for 4.19. > > Ingo, see below for a patch to pick up into -tip when you have a chance. > >> >> Without this patch, dm-writecache is suffering 2% penalty because of >> memcpy_flushcache overhead. >> >> Mikulas >> >> >> >> From: Mikulas Patocka <mpatocka@redhat.com> >> >> 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 <mpatocka@redhat.com> >> >> --- >> 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 > Linux-nvdimm@lists.01.org > https://lists.01.org/mailman/listinfo/linux-nvdimm
On Wed, Jun 27, 2018 at 4:23 AM, Yigal Korman <yigal@plexistor.com> wrote: > Hi, > I'm a bit late on this but I have a question about the original patch - > I thought that in order for movnt (movntil, movntiq) to push the data > into the persistency domain (ADR), > one must work with length that is multiple of cacheline size, > otherwise the write-combine buffers remain partially > filled and you need to commit them with a fence (sfence) - which ruins > the whole performance gain you got here. > Am I wrong, are the write-combine buffers are part of the ADR domain > or something? The intent is to allow a batch of memcpy_flushcache() calls followed by a single sfence. Specifying a multiple of a cacheline size does not necessarily help as sfence is still needed to make sure that the movnt result has reached the ADR-safe domain.
On Wed, Jun 27, 2018 at 4:03 PM, Dan Williams <dan.j.williams@intel.com> wrote: > On Wed, Jun 27, 2018 at 4:23 AM, Yigal Korman <yigal@plexistor.com> wrote: >> Hi, >> I'm a bit late on this but I have a question about the original patch - >> I thought that in order for movnt (movntil, movntiq) to push the data >> into the persistency domain (ADR), >> one must work with length that is multiple of cacheline size, >> otherwise the write-combine buffers remain partially >> filled and you need to commit them with a fence (sfence) - which ruins >> the whole performance gain you got here. >> Am I wrong, are the write-combine buffers are part of the ADR domain >> or something? > > The intent is to allow a batch of memcpy_flushcache() calls followed > by a single sfence. Specifying a multiple of a cacheline size does not > necessarily help as sfence is still needed to make sure that the movnt > result has reached the ADR-safe domain. Oh, right, I see that dm-writecache calls writecache_commit_flushed which in turn calls wmb(). I keep confusing *_nocache (i.e. copy_user_nocache) that includes sfence and *_flushcache (i.e. memcpy_flushcache) that doesn't. Thanks for the clear up.
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)