[PATCH] arm64: lib: improve usercopy performance by mitigating data dependencies
From: Li Zetao
Date: Tue Mar 12 2024 - 11:09:16 EST
In the copy_from/to_user scenario, due to the need to accurately
calculate the number of copied bytes for fixup, it is necessary to
increment the values of src and dst after each copy of the data.
Therefore, this introduce RAW dependency which result in some bubble
in pipline and degrade the IPC.
Consider updating the values of src and dst only when the copy is
completed in the current stage to reduce data dependence. But this will
break the function of fixup, so in order to maintain the function of
fixup, a new variable is introduced to record the number of bytes to be
copied in the current stage. Once an access exception occurs, the variable
can be used to determined the final index of access exception by copying
byte-by-byte.
Here are the test result:
Copy 128 bytes cost on Kunpeng-920(us):
Without this patch:
copy_from_user: 1.0187 copy_to_user: 1.1021
With this patch:
copy_from_user: 0.9523 copy_to_user: 1.0159
It's about 7% improvement in copy_from/to_user()
Signed-off-by: Li Zetao <lizetao1@xxxxxxxxxx>
---
arch/arm64/include/asm/asm-uaccess.h | 14 +++---
arch/arm64/lib/copy_from_user.S | 21 +++++++--
arch/arm64/lib/copy_template.S | 66 +++++++++++++++++-----------
arch/arm64/lib/copy_to_user.S | 22 +++++++---
4 files changed, 81 insertions(+), 42 deletions(-)
diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
index 5b6efe8abeeb..ccbde0d0c113 100644
--- a/arch/arm64/include/asm/asm-uaccess.h
+++ b/arch/arm64/include/asm/asm-uaccess.h
@@ -66,19 +66,17 @@ alternative_else_nop_endif
* This is complicated as there is no post-increment or pair versions of the
* unprivileged instructions, and USER() only works for single instructions.
*/
- .macro user_ldp l, reg1, reg2, addr, post_inc
-8888: ldtr \reg1, [\addr];
-8889: ldtr \reg2, [\addr, #8];
- add \addr, \addr, \post_inc;
+ .macro user_ldp l, reg1, reg2, addr, offs_inc
+8888: ldtr \reg1, [\addr, \offs_inc];
+8889: ldtr \reg2, [\addr, \offs_inc + 8];
_asm_extable_uaccess 8888b, \l;
_asm_extable_uaccess 8889b, \l;
.endm
- .macro user_stp l, reg1, reg2, addr, post_inc
-8888: sttr \reg1, [\addr];
-8889: sttr \reg2, [\addr, #8];
- add \addr, \addr, \post_inc;
+ .macro user_stp l, reg1, reg2, addr, offs_inc
+8888: sttr \reg1, [\addr, \offs_inc];
+8889: sttr \reg2, [\addr, \offs_inc + 8];
_asm_extable_uaccess 8888b,\l;
_asm_extable_uaccess 8889b,\l;
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 34e317907524..c575829b85be 100644
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -49,7 +49,7 @@
.endm
.macro stp1 reg1, reg2, ptr, val
- stp \reg1, \reg2, [\ptr], \val
+ stp \reg1, \reg2, [\ptr, \val]
.endm
end .req x5
@@ -62,12 +62,25 @@ SYM_FUNC_START(__arch_copy_from_user)
ret
// Exception fixups
-9997: cmp dst, dstin
+9997: sub x7, src, srcin
+ sub x8, dst, dstin
+ cmp x7, x8
+ b.le no_need_to_adjust_src
+ sub x9, x7, x8
+ sub src, src, p_copy
+ add p_copy, p_copy, x9
+no_need_to_adjust_src:
+ cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
-USER(9998f, ldtrb tmp1w, [srcin])
+calculate_bytes_copied:
+USER(9999f, ldtrb tmp1w, [src])
strb tmp1w, [dst], #1
-9998: sub x0, end, dst // bytes not copied
+ add src, src, #1
+ sub p_copy, p_copy, #1
+9998: cmp p_copy, 0
+ b.ge calculate_bytes_copied
+9999: sub x0, end, dst // bytes not copied
ret
SYM_FUNC_END(__arch_copy_from_user)
EXPORT_SYMBOL(__arch_copy_from_user)
diff --git a/arch/arm64/lib/copy_template.S b/arch/arm64/lib/copy_template.S
index 488df234c49a..8832b9fd0257 100644
--- a/arch/arm64/lib/copy_template.S
+++ b/arch/arm64/lib/copy_template.S
@@ -29,6 +29,7 @@ tmp1w .req w3
tmp2 .req x4
tmp2w .req w4
dst .req x6
+p_copy .req x16
A_l .req x7
A_h .req x8
@@ -39,6 +40,7 @@ C_h .req x12
D_l .req x13
D_h .req x14
+ mov p_copy, 16
mov dst, dstin
cmp count, #16
/*When memory length is less than 16, the accessed are not aligned.*/
@@ -82,19 +84,26 @@ D_h .req x14
* Copy up to 48 bytes of data. At this point we only need the
* bottom 6 bits of count to be accurate.
*/
+ mov p_copy, #16
ands tmp1, count, #0x30
b.eq .Ltiny15
cmp tmp1w, #0x20
b.eq 1f
b.lt 2f
- ldp1 A_l, A_h, src, #16
- stp1 A_l, A_h, dst, #16
+ ldp1 A_l, A_h, src, #0
+ stp1 A_l, A_h, dst, #0
+ add src, src, #16
+ add dst, dst, #16
1:
- ldp1 A_l, A_h, src, #16
- stp1 A_l, A_h, dst, #16
+ ldp1 A_l, A_h, src, #0
+ stp1 A_l, A_h, dst, #0
+ add src, src, #16
+ add dst, dst, #16
2:
- ldp1 A_l, A_h, src, #16
- stp1 A_l, A_h, dst, #16
+ ldp1 A_l, A_h, src, #0
+ stp1 A_l, A_h, dst, #0
+ add src, src, #16
+ add dst, dst, #16
.Ltiny15:
/*
* Prefer to break one ldp/stp into several load/store to access
@@ -126,20 +135,23 @@ D_h .req x14
b .Lexitfunc
.Lcpy_over64:
+ mov p_copy, #64
subs count, count, #128
b.ge .Lcpy_body_large
/*
* Less than 128 bytes to copy, so handle 64 here and then jump
* to the tail.
*/
- ldp1 A_l, A_h, src, #16
- stp1 A_l, A_h, dst, #16
+ ldp1 A_l, A_h, src, #0
+ stp1 A_l, A_h, dst, #0
ldp1 B_l, B_h, src, #16
- ldp1 C_l, C_h, src, #16
+ ldp1 C_l, C_h, src, #32
stp1 B_l, B_h, dst, #16
- stp1 C_l, C_h, dst, #16
- ldp1 D_l, D_h, src, #16
- stp1 D_l, D_h, dst, #16
+ stp1 C_l, C_h, dst, #32
+ ldp1 D_l, D_h, src, #48
+ stp1 D_l, D_h, dst, #48
+ add src, src, #64
+ add dst, dst, #64
tst count, #0x3f
b.ne .Ltail63
@@ -152,30 +164,34 @@ D_h .req x14
.p2align L1_CACHE_SHIFT
.Lcpy_body_large:
/* pre-get 64 bytes data. */
- ldp1 A_l, A_h, src, #16
+ ldp1 A_l, A_h, src, #0
ldp1 B_l, B_h, src, #16
- ldp1 C_l, C_h, src, #16
- ldp1 D_l, D_h, src, #16
+ ldp1 C_l, C_h, src, #32
+ ldp1 D_l, D_h, src, #48
+ add src, src, #64
1:
/*
* interlace the load of next 64 bytes data block with store of the last
* loaded 64 bytes data.
*/
- stp1 A_l, A_h, dst, #16
- ldp1 A_l, A_h, src, #16
+ stp1 A_l, A_h, dst, #0
+ ldp1 A_l, A_h, src, #0
stp1 B_l, B_h, dst, #16
ldp1 B_l, B_h, src, #16
- stp1 C_l, C_h, dst, #16
- ldp1 C_l, C_h, src, #16
- stp1 D_l, D_h, dst, #16
- ldp1 D_l, D_h, src, #16
+ stp1 C_l, C_h, dst, #32
+ ldp1 C_l, C_h, src, #32
+ stp1 D_l, D_h, dst, #48
+ ldp1 D_l, D_h, src, #48
+ add src, src, #64
+ add dst, dst, #64
subs count, count, #64
b.ge 1b
- stp1 A_l, A_h, dst, #16
+ stp1 A_l, A_h, dst, #0
stp1 B_l, B_h, dst, #16
- stp1 C_l, C_h, dst, #16
- stp1 D_l, D_h, dst, #16
+ stp1 C_l, C_h, dst, #32
+ stp1 D_l, D_h, dst, #48
+ add dst, dst, #64
tst count, #0x3f
b.ne .Ltail63
-.Lexitfunc:
+.Lexitfunc: mov p_copy, #0
diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 802231772608..89db19e09ca2 100644
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S
@@ -44,7 +44,7 @@
.endm
.macro ldp1 reg1, reg2, ptr, val
- ldp \reg1, \reg2, [\ptr], \val
+ ldp \reg1, \reg2, [\ptr, \val]
.endm
.macro stp1 reg1, reg2, ptr, val
@@ -61,13 +61,25 @@ SYM_FUNC_START(__arch_copy_to_user)
ret
// Exception fixups
-9997: cmp dst, dstin
+9997: sub x7, src, srcin
+ sub x8, dst, dstin
+ cmp x7, x8
+ b.le no_need_to_adjust_src
+ sub x9, x7, x8
+ sub src, src, x9
+ add p_copy, p_copy, x9
+no_need_to_adjust_src:
+ cmp dst, dstin
b.ne 9998f
// Before being absolutely sure we couldn't copy anything, try harder
- ldrb tmp1w, [srcin]
-USER(9998f, sttrb tmp1w, [dst])
+calculate_bytes_copied:
+ ldrb tmp1w, [src], #1
+USER(9999f, sttrb tmp1w, [dst])
add dst, dst, #1
-9998: sub x0, end, dst // bytes not copied
+ sub p_copy, p_copy, #1
+9998: cmp p_copy, 0
+ b.ge calculate_bytes_copied
+9999: sub x0, end, dst // bytes not copied
ret
SYM_FUNC_END(__arch_copy_to_user)
EXPORT_SYMBOL(__arch_copy_to_user)
--
2.34.1