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SubjectRe: [PATCH 0/13] Parallel struct page initialisation v3
On Thu, Apr 23, 2015 at 6:33 PM, Mel Gorman <mgorman@suse.de> wrote:
> The big change here is an adjustment to the topology_init path that
> caused
> soft lockups on Waiman and Daniel Blue had reported it was an
> expensive
> function.
>
> Changelog since v2
> o Reduce overhead of topology_init
> o Remove boot-time kernel parameter to enable/disable
> o Enable on UMA
>
> Changelog since v1
> o Always initialise low zones
> o Typo corrections
> o Rename parallel mem init to parallel struct page init
> o Rebase to 4.0
[]

Splendid work! On this 256c setup, topology_init now takes 185ms.

This brings the kernel boot time down to 324s [1]. It turns out that
one memset is responsible for most of the time setting up the the PUDs
and PMDs; adapting memset to using non-temporal writes [3] avoids
generating RMW cycles, bringing boot time down to 186s [2].

If this is a possibility, I can split this patch and map other arch's
memset_nocache to memset, or change the callsite as preferred; comments
welcome.

Thanks,
Daniel

[1] https://resources.numascale.com/telemetry/defermem/h8qgl-defer2.txt
[2]
https://resources.numascale.com/telemetry/defermem/h8qgl-defer2-nontemporal.txt

-- [3]

From f822139736cab8434302693c635fa146b465273c Mon Sep 17 00:00:00 2001
From: Daniel J Blueman <daniel@numascale.com>
Date: Thu, 23 Apr 2015 23:26:27 +0800
Subject: [RFC] Speedup PMD setup

Using non-temporal writes prevents read-modify-write cycles,
which are much slower over large topologies.

Adapt the existing memset() function into a _nocache variant and use
when setting up PMDs during early boot to reduce boot time.

Signed-off-by: Daniel J Blueman <daniel@numascale.com>
---
arch/x86/include/asm/string_64.h | 3 ++
arch/x86/lib/memset_64.S | 90
++++++++++++++++++++++++++++++++++++++++
mm/memblock.c | 2 +-
3 files changed, 94 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/string_64.h
b/arch/x86/include/asm/string_64.h
index e466119..1ef28d0 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -55,6 +55,8 @@ extern void *memcpy(void *to, const void *from,
size_t len);
#define __HAVE_ARCH_MEMSET
void *memset(void *s, int c, size_t n);
void *__memset(void *s, int c, size_t n);
+void *memset_nocache(void *s, int c, size_t n);
+void *__memset_nocache(void *s, int c, size_t n);

#define __HAVE_ARCH_MEMMOVE
void *memmove(void *dest, const void *src, size_t count);
@@ -77,6 +79,7 @@ int strcmp(const char *cs, const char *ct);
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
+#define memset_nocache(s, c, n) __memset_nocache(s, c, n)
#endif

#endif /* __KERNEL__ */
diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
index 6f44935..fb46f78 100644
--- a/arch/x86/lib/memset_64.S
+++ b/arch/x86/lib/memset_64.S
@@ -137,6 +137,96 @@ ENTRY(__memset)
ENDPROC(memset)
ENDPROC(__memset)

+/*
+ * bzero_nocache - set a memory block to zero. This function uses
+ * non-temporal writes in the fastpath
+ *
+ * rdi destination
+ * rsi value (char)
+ * rdx count (bytes)
+ *
+ * rax original destination
+ */
+
+ENTRY(memset_nocache)
+ENTRY(__memset_nocache)
+ CFI_STARTPROC
+ movq %rdi,%r10
+
+ /* expand byte value */
+ movzbl %sil,%ecx
+ movabs $0x0101010101010101,%rax
+ imulq %rcx,%rax
+
+ /* align dst */
+ movl %edi,%r9d
+ andl $7,%r9d
+ jnz bad_alignment
+ CFI_REMEMBER_STATE
+after_bad_alignment:
+
+ movq %rdx,%rcx
+ shrq $6,%rcx
+ jz handle_tail
+
+ .p2align 4
+loop_64:
+ decq %rcx
+ movnti %rax,(%rdi)
+ movnti %rax,8(%rdi)
+ movnti %rax,16(%rdi)
+ movnti %rax,24(%rdi)
+ movnti %rax,32(%rdi)
+ movnti %rax,40(%rdi)
+ movnti %rax,48(%rdi)
+ movnti %rax,56(%rdi)
+ leaq 64(%rdi),%rdi
+ jnz loop_64
+
+ /* Handle tail in loops; the loops should be faster than hard
+ to predict jump tables */
+ .p2align 4
+handle_tail:
+ movl %edx,%ecx
+ andl $63&(~7),%ecx
+ jz handle_7
+ shrl $3,%ecx
+ .p2align 4
+loop_8:
+ decl %ecx
+ movnti %rax,(%rdi)
+ leaq 8(%rdi),%rdi
+ jnz loop_8
+
+handle_7:
+ andl $7,%edx
+ jz ende
+ .p2align 4
+loop_1:
+ decl %edx
+ movb %al,(%rdi)
+ leaq 1(%rdi),%rdi
+ jnz loop_1
+
+ende:
+ movq %r10,%rax
+ ret
+
+ CFI_RESTORE_STATE
+bad_alignment:
+ cmpq $7,%rdx
+ jbe handle_7
+ movnti %rax,(%rdi) /* unaligned store */
+ movq $8,%r8
+ subq %r9,%r8
+ addq %r8,%rdi
+ subq %r8,%rdx
+ jmp after_bad_alignment
+final:
+ CFI_ENDPROC
+ENDPROC(memset_nocache)
+ENDPROC(__memset_nocache)
+
/* Some CPUs support enhanced REP MOVSB/STOSB feature.
* It is recommended to use this when possible.
*
diff --git a/mm/memblock.c b/mm/memblock.c
index f3e97d8..df434d2 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1212,7 +1212,7 @@ again:
done:
memblock_reserve(alloc, size);
ptr = phys_to_virt(alloc);
- memset(ptr, 0, size);
+ memset_nocache(ptr, 0, size);

/*
* The min_count is set to 0 so that bootmem allocated blocks


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