From: Mikulas Patocka <mpatocka@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Dan Williams <dan.j.williams@intel.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
device-mapper development <dm-devel@redhat.com>
Subject: [PATCH v2] x86: introduce memcpy_flushcache_single
Date: Mon, 20 Apr 2020 09:47:54 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.2004200943160.4909@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <87a739zvrg.fsf@nanos.tec.linutronix.de>
On Fri, 17 Apr 2020, Thomas Gleixner wrote:
> Dan Williams <dan.j.williams@intel.com> writes:
>
> > The goal of naming it _inatomic() was specifically for the observation
> > that your driver coordinates atomic access and does not benefit from
> > the cache friendliness that non-temporal stores afford. That said
> > _inatomic() is arguably not a good choice either because that refers
> > to whether the copy is prepared to take a fault or not. What about
> > _exclusive() or _single()? Anything but _clflushopt() that conveys no
> > contextual information.
OK. I renamed it to memcpy_flushcache_single
> > Other than quibbling with the name, and one more comment below, this
> > looks ok to me.
> >
> >> Index: linux-2.6/drivers/md/dm-writecache.c
> >> ===================================================================
> >> --- linux-2.6.orig/drivers/md/dm-writecache.c 2020-04-17 14:06:35.139999000 +0200
> >> +++ linux-2.6/drivers/md/dm-writecache.c 2020-04-17 14:06:35.129999000 +0200
> >> @@ -1166,7 +1166,10 @@ static void bio_copy_block(struct dm_wri
> >> }
> >> } else {
> >> flush_dcache_page(bio_page(bio));
> >> - memcpy_flushcache(data, buf, size);
> >> + if (likely(size > 512))
> >
> > This needs some reference to how this magic number is chosen and how a
> > future developer might determine whether the value needs to be
> > adjusted.
>
> I don't think it's a good idea to make this decision in generic code as
> architectures or even CPU models might have different constraints on the
> size.
>
> So I'd rather let the architecture implementation decide and make this
>
> flush_dcache_page(bio_page(bio));
> - memcpy_flushcache(data, buf, size);
> + memcpy_flushcache_bikesheddedname(data, buf, size);
>
> and have the default fallback memcpy_flushcache() and let the
> architecture sort the size limit and the underlying technology out.
>
> So x86 can use clflushopt or implement it with movdir64b and any other
> architecture can provide their own magic soup without changing the
> callsite.
>
> Thanks,
>
> tglx
OK - so I moved the decision to memcpy_flushcache_single and I added a
comment that explains the magic number.
Mikulas
From: Mikulas Patocka <mpatocka@redhat.com>
Implement the function memcpy_flushcache_single which flushes cache just
like memcpy_flushcache - except that it uses cached writes and explicit
cache flushing instead of non-temporal stores.
Explicit cache flushing performs better in singlethreaded cases (i.e. the
dm-writecache target with block size greater than 512), non-temporal
stores perform better in other cases (mostly multithreaded workloads) - so
we provide these two functions and the user should select which one is
faster for his particular workload.
dm-writecache througput (on real Optane-based persistent memory):
block size 512 1024 2048 4096
movnti 496 MB/s 642 MB/s 725 MB/s 744 MB/s
clflushopt 373 MB/s 688 MB/s 1.1 GB/s 1.2 GB/s
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
---
arch/x86/include/asm/string_64.h | 10 ++++++++
arch/x86/lib/usercopy_64.c | 46 +++++++++++++++++++++++++++++++++++++++
drivers/md/dm-writecache.c | 2 -
include/linux/string.h | 6 +++++
4 files changed, 63 insertions(+), 1 deletion(-)
Index: linux-2.6/arch/x86/include/asm/string_64.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/string_64.h 2020-04-20 15:31:46.939999000 +0200
+++ linux-2.6/arch/x86/include/asm/string_64.h 2020-04-20 15:31:46.929999000 +0200
@@ -114,6 +114,14 @@ memcpy_mcsafe(void *dst, const void *src
return 0;
}
+/*
+ * In some cases (mostly single-threaded workload), clflushopt is faster
+ * than non-temporal stores. In other situations, non-temporal stores are
+ * faster. So, we provide two functions:
+ * memcpy_flushcache using non-temporal stores
+ * memcpy_flushcache_single using clflushopt
+ * The caller should test which one is faster for the particular workload.
+ */
#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
#define __HAVE_ARCH_MEMCPY_FLUSHCACHE 1
void __memcpy_flushcache(void *dst, const void *src, size_t cnt);
@@ -135,6 +143,8 @@ static __always_inline void memcpy_flush
}
__memcpy_flushcache(dst, src, cnt);
}
+#define __HAVE_ARCH_MEMCPY_FLUSHCACHE_CLFLUSHOPT 1
+void memcpy_flushcache_single(void *dst, const void *src, size_t cnt);
#endif
#endif /* __KERNEL__ */
Index: linux-2.6/include/linux/string.h
===================================================================
--- linux-2.6.orig/include/linux/string.h 2020-04-20 15:31:46.939999000 +0200
+++ linux-2.6/include/linux/string.h 2020-04-20 15:31:46.929999000 +0200
@@ -175,6 +175,12 @@ static inline void memcpy_flushcache(voi
memcpy(dst, src, cnt);
}
#endif
+#ifndef __HAVE_ARCH_MEMCPY_FLUSHCACHE_CLFLUSHOPT
+static inline void memcpy_flushcache_single(void *dst, const void *src, size_t cnt)
+{
+ memcpy_flushcache(dst, src, cnt);
+}
+#endif
void *memchr_inv(const void *s, int c, size_t n);
char *strreplace(char *s, char old, char new);
Index: linux-2.6/arch/x86/lib/usercopy_64.c
===================================================================
--- linux-2.6.orig/arch/x86/lib/usercopy_64.c 2020-04-20 15:31:46.939999000 +0200
+++ linux-2.6/arch/x86/lib/usercopy_64.c 2020-04-20 15:38:13.159999000 +0200
@@ -199,6 +199,52 @@ void __memcpy_flushcache(void *_dst, con
}
EXPORT_SYMBOL_GPL(__memcpy_flushcache);
+void memcpy_flushcache_single(void *_dst, const void *_src, size_t size)
+{
+ unsigned long dest = (unsigned long) _dst;
+ unsigned long source = (unsigned long) _src;
+
+ /*
+ * dm-writecache througput (on real Optane-based persistent memory):
+ * measured with dd:
+ *
+ * block size 512 1024 2048 4096
+ * movnti 496 MB/s 642 MB/s 725 MB/s 744 MB/s
+ * clflushopt 373 MB/s 688 MB/s 1.1 GB/s 1.2 GB/s
+ *
+ * We see that movnti performs better for 512-byte blocks, and
+ * clflushopt performs better for 1024-byte and larger blocks. So, we
+ * prefer clflushopt for sizes >= 768.
+ */
+
+ if (static_cpu_has(X86_FEATURE_CLFLUSHOPT) && likely(boot_cpu_data.x86_clflush_size == 64) &&
+ likely(size >= 768)) {
+ if (unlikely(!IS_ALIGNED(dest, 64))) {
+ size_t len = min_t(size_t, size, ALIGN(dest, 64) - dest);
+
+ memcpy((void *) dest, (void *) source, len);
+ clflushopt((void *)dest);
+ dest += len;
+ source += len;
+ size -= len;
+ }
+ do {
+ memcpy((void *)dest, (void *)source, 64);
+ clflushopt((void *)dest);
+ dest += 64;
+ source += 64;
+ size -= 64;
+ } while (size >= 64)
+ if (unlikely(size != 0)) {
+ memcpy((void *)dest, (void *)source, size);
+ clflushopt((void *)dest);
+ }
+ return;
+ }
+ memcpy_flushcache((void *)dest, (void *)source, size);
+}
+EXPORT_SYMBOL_GPL(memcpy_flushcache_single);
+
void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
size_t len)
{
Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c 2020-04-20 15:31:46.939999000 +0200
+++ linux-2.6/drivers/md/dm-writecache.c 2020-04-20 15:32:35.549999000 +0200
@@ -1166,7 +1166,7 @@ static void bio_copy_block(struct dm_wri
}
} else {
flush_dcache_page(bio_page(bio));
- memcpy_flushcache(data, buf, size);
+ memcpy_flushcache_single(data, buf, size);
}
bvec_kunmap_irq(buf, &flags);
next prev parent reply other threads:[~2020-04-20 13:48 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-07 15:01 [PATCH] memcpy_flushcache: use cache flusing for larger lengths Mikulas Patocka
2020-04-07 16:09 ` Andy Lutomirski
2020-04-07 16:33 ` Mikulas Patocka
2020-04-07 17:52 ` Dan Williams
2020-04-08 18:54 ` Mikulas Patocka
2020-04-08 19:29 ` Dan Williams
2020-04-09 14:36 ` Mikulas Patocka
2020-04-16 8:24 ` Mikulas Patocka
2020-04-16 8:24 ` Mikulas Patocka
2020-04-16 18:28 ` Dan Williams
2020-04-17 12:47 ` [PATCH] x86: introduce memcpy_flushcache_clflushopt Mikulas Patocka
2020-04-17 17:57 ` Dan Williams
2020-04-17 20:45 ` Thomas Gleixner
2020-04-20 13:47 ` Mikulas Patocka [this message]
2020-04-21 18:43 ` [PATCH v2] x86: introduce memcpy_flushcache_single Dan Williams
2020-04-18 13:27 ` [PATCH] x86: introduce memcpy_flushcache_clflushopt David Laight
2020-04-18 15:21 ` Mikulas Patocka
2020-04-19 17:48 ` David Laight
2020-04-20 4:49 ` Dan Williams
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.LRH.2.02.2004200943160.4909@file01.intranet.prod.int.rdu2.redhat.com \
--to=mpatocka@redhat.com \
--cc=bp@alien8.de \
--cc=dan.j.williams@intel.com \
--cc=dm-devel@redhat.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.