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Subject[PATCH v2 1/5] ARCv2: lib: memcpy: fix doing prefetchw outside of buffer
Date
ARCv2 optimized memcpy uses PREFETCHW instruction for prefetching the
next cache line but doesn't ensure that the line is not past the end of
the buffer. PRETECHW changes the line ownership and marks it dirty,
which can cause data corruption if this area is used for DMA IO.

Fix the issue by avoiding the PREFETCHW. This leads to performance
degradation but it is OK as we'll introduce new memcpy implementation
optimized for unaligned memory access using.

We also cut off all PREFETCH instructions at they are quite useless
here:
* we call PREFETCH right before LOAD instruction call.
* we copy 16 or 32 bytes of data (depending on CONFIG_ARC_HAS_LL64)
in a main logical loop. so we call PREFETCH 4 times (or 2 times)
for each L1 cache line (in case of 64B L1 cache Line which is
default case). Obviously this is not optimal.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
---
arch/arc/lib/memcpy-archs.S | 14 --------------
1 file changed, 14 deletions(-)

diff --git a/arch/arc/lib/memcpy-archs.S b/arch/arc/lib/memcpy-archs.S
index d61044dd8b58..ea14b0bf3116 100644
--- a/arch/arc/lib/memcpy-archs.S
+++ b/arch/arc/lib/memcpy-archs.S
@@ -25,15 +25,11 @@
#endif

#ifdef CONFIG_ARC_HAS_LL64
-# define PREFETCH_READ(RX) prefetch [RX, 56]
-# define PREFETCH_WRITE(RX) prefetchw [RX, 64]
# define LOADX(DST,RX) ldd.ab DST, [RX, 8]
# define STOREX(SRC,RX) std.ab SRC, [RX, 8]
# define ZOLSHFT 5
# define ZOLAND 0x1F
#else
-# define PREFETCH_READ(RX) prefetch [RX, 28]
-# define PREFETCH_WRITE(RX) prefetchw [RX, 32]
# define LOADX(DST,RX) ld.ab DST, [RX, 4]
# define STOREX(SRC,RX) st.ab SRC, [RX, 4]
# define ZOLSHFT 4
@@ -41,8 +37,6 @@
#endif

ENTRY_CFI(memcpy)
- prefetch [r1] ; Prefetch the read location
- prefetchw [r0] ; Prefetch the write location
mov.f 0, r2
;;; if size is zero
jz.d [blink]
@@ -72,8 +66,6 @@ ENTRY_CFI(memcpy)
lpnz @.Lcopy32_64bytes
;; LOOP START
LOADX (r6, r1)
- PREFETCH_READ (r1)
- PREFETCH_WRITE (r3)
LOADX (r8, r1)
LOADX (r10, r1)
LOADX (r4, r1)
@@ -117,9 +109,7 @@ ENTRY_CFI(memcpy)
lpnz @.Lcopy8bytes_1
;; LOOP START
ld.ab r6, [r1, 4]
- prefetch [r1, 28] ;Prefetch the next read location
ld.ab r8, [r1,4]
- prefetchw [r3, 32] ;Prefetch the next write location

SHIFT_1 (r7, r6, 24)
or r7, r7, r5
@@ -162,9 +152,7 @@ ENTRY_CFI(memcpy)
lpnz @.Lcopy8bytes_2
;; LOOP START
ld.ab r6, [r1, 4]
- prefetch [r1, 28] ;Prefetch the next read location
ld.ab r8, [r1,4]
- prefetchw [r3, 32] ;Prefetch the next write location

SHIFT_1 (r7, r6, 16)
or r7, r7, r5
@@ -204,9 +192,7 @@ ENTRY_CFI(memcpy)
lpnz @.Lcopy8bytes_3
;; LOOP START
ld.ab r6, [r1, 4]
- prefetch [r1, 28] ;Prefetch the next read location
ld.ab r8, [r1,4]
- prefetchw [r3, 32] ;Prefetch the next write location

SHIFT_1 (r7, r6, 8)
or r7, r7, r5
--
2.14.5
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