From: Mikulas Patocka <mpatocka@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org, Dan Williams <dan.j.williams@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dm-devel@redhat.com
Subject: [PATCH] memcpy_flushcache: use cache flusing for larger lengths
Date: Tue, 7 Apr 2020 11:01:33 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.2004071029270.8662@file01.intranet.prod.int.rdu2.redhat.com> (raw)
[ resending this to x86 maintainers ]
Hi
I tested performance of various methods how to write to optane-based
persistent memory, and found out that non-temporal stores achieve
throughput 1.3 GB/s. 8 cached stores immediatelly followed by clflushopt
or clwb achieve throughput 1.6 GB/s.
memcpy_flushcache uses non-temporal stores, I modified it to use cached
stores + clflushopt and it improved performance of the dm-writecache
target significantly:
dm-writecache throughput:
(dd if=/dev/zero of=/dev/mapper/wc bs=64k oflag=direct)
writecache 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
For block size 512, movnti works better, for larger block sizes,
clflushopt is better.
I was also testing the novafs filesystem, it is not upstream, but it
benefitted from similar change in __memcpy_flushcache and
__copy_user_nocache:
write throughput on big files - movnti: 662 MB/s, clwb: 1323 MB/s
write throughput on small files - movnti: 621 MB/s, clwb: 1013 MB/s
I submit this patch for __memcpy_flushcache that improves dm-writecache
performance.
Other ideas - should we introduce memcpy_to_pmem instead of modifying
memcpy_flushcache and move this logic there? Or should I modify the
dm-writecache target directly to use clflushopt with no change to the
architecture-specific code?
Mikulas
From: Mikulas Patocka <mpatocka@redhat.com>
I tested dm-writecache performance on a machine with Optane nvdimm and it
turned out that for larger writes, cached stores + cache flushing perform
better than non-temporal stores. This is the throughput of dm-writecache
measured with this command:
dd if=/dev/zero of=/dev/mapper/wc bs=64 oflag=direct
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 can see that for smaller block, movnti performs better, but for larger
blocks, clflushopt has better performance.
This patch changes the function __memcpy_flushcache accordingly, so that
with size >= 768 it performs cached stores and cache flushing. Note that
we must not use the new branch if the CPU doesn't have clflushopt - in
that case, the kernel would use inefficient "clflush" instruction that has
very bad performance.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
---
arch/x86/lib/usercopy_64.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
Index: linux-2.6/arch/x86/lib/usercopy_64.c
===================================================================
--- linux-2.6.orig/arch/x86/lib/usercopy_64.c 2020-03-24 15:15:36.644945091 -0400
+++ linux-2.6/arch/x86/lib/usercopy_64.c 2020-03-30 07:17:51.450290007 -0400
@@ -152,6 +152,42 @@ void __memcpy_flushcache(void *_dst, con
return;
}
+ if (static_cpu_has(X86_FEATURE_CLFLUSHOPT) && size >= 768 && likely(boot_cpu_data.x86_clflush_size == 64)) {
+ while (!IS_ALIGNED(dest, 64)) {
+ asm("movq (%0), %%r8\n"
+ "movnti %%r8, (%1)\n"
+ :: "r" (source), "r" (dest)
+ : "memory", "r8");
+ dest += 8;
+ source += 8;
+ size -= 8;
+ }
+ do {
+ asm("movq (%0), %%r8\n"
+ "movq 8(%0), %%r9\n"
+ "movq 16(%0), %%r10\n"
+ "movq 24(%0), %%r11\n"
+ "movq %%r8, (%1)\n"
+ "movq %%r9, 8(%1)\n"
+ "movq %%r10, 16(%1)\n"
+ "movq %%r11, 24(%1)\n"
+ "movq 32(%0), %%r8\n"
+ "movq 40(%0), %%r9\n"
+ "movq 48(%0), %%r10\n"
+ "movq 56(%0), %%r11\n"
+ "movq %%r8, 32(%1)\n"
+ "movq %%r9, 40(%1)\n"
+ "movq %%r10, 48(%1)\n"
+ "movq %%r11, 56(%1)\n"
+ :: "r" (source), "r" (dest)
+ : "memory", "r8", "r9", "r10", "r11");
+ clflushopt((void *)dest);
+ dest += 64;
+ source += 64;
+ size -= 64;
+ } while (size >= 64);
+ }
+
/* 4x8 movnti loop */
while (size >= 32) {
asm("movq (%0), %%r8\n"
next reply other threads:[~2020-04-07 15:01 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-07 15:01 Mikulas Patocka [this message]
2020-04-07 16:09 ` [PATCH] memcpy_flushcache: use cache flusing for larger lengths 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 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 ` [PATCH v2] x86: introduce memcpy_flushcache_single Mikulas Patocka
2020-04-21 18:43 ` 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
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