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mundaym opened this issue Sep 8, 2021 · 7 comments
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runtime: memmove executes unaligned accesses on riscv64 #48248

mundaym opened this issue Sep 8, 2021 · 7 comments
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@mundaym
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arch-riscv Issues solely affecting the riscv64 architecture. compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge Performance
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Go1.20

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@mundaym
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mundaym commented Sep 8, 2021

The performance of memmove when copying more than ~16 bytes of unaligned data is very poor on the HiFive Unmatched. Looking at the code it only attempts to align the source operand before using word-sized load and store operations. This means that stores to the destination operand will be unaligned. On the HiFive Unmatched unaligned accesses result in a trap that is handled by the kernel and so performance is extremely poor (~10x slower than performing a byte-by-byte copy).

Benchmarks:

name                               speed
Memmove/0-4
Memmove/1-4                        37.0MB/s ± 5%
Memmove/2-4                        55.6MB/s ± 8%
Memmove/3-4                        67.2MB/s ± 5%
Memmove/4-4                        85.5MB/s ± 6%
Memmove/5-4                        98.1MB/s ± 6%
Memmove/6-4                         112MB/s ± 3%
Memmove/7-4                         127MB/s ± 4%
Memmove/8-4                         241MB/s ± 3%
Memmove/9-4                         229MB/s ± 7%
Memmove/10-4                        230MB/s ± 9%
Memmove/11-4                        198MB/s ± 5%
Memmove/12-4                        202MB/s ± 3%
Memmove/13-4                        206MB/s ± 4%
Memmove/14-4                        212MB/s ± 3%
Memmove/15-4                        213MB/s ± 6%
Memmove/16-4                        407MB/s ± 4%
Memmove/32-4                        577MB/s ± 3%
Memmove/64-4                        890MB/s ± 4%
Memmove/128-4                      1.28GB/s ± 6%
Memmove/256-4                      1.52GB/s ± 5%
Memmove/512-4                      1.67GB/s ± 2%
Memmove/1024-4                     1.81GB/s ± 2%
Memmove/2048-4                     1.91GB/s ± 1%
Memmove/4096-4                     1.94GB/s ± 1%
MemmoveOverlap/32-4                 485MB/s ± 5%
MemmoveOverlap/64-4                 694MB/s ± 6%
MemmoveOverlap/128-4                899MB/s ± 3%
MemmoveOverlap/256-4               1.06GB/s ± 3%
MemmoveOverlap/512-4               1.18GB/s ± 2%
MemmoveOverlap/1024-4              1.24GB/s ± 1%
MemmoveOverlap/2048-4              1.28GB/s ± 1%
MemmoveOverlap/4096-4              1.30GB/s ± 1%
MemmoveUnalignedDst/0-4
MemmoveUnalignedDst/1-4            31.6MB/s ± 5%
MemmoveUnalignedDst/2-4            54.1MB/s ±12%
MemmoveUnalignedDst/3-4            66.2MB/s ±10%
MemmoveUnalignedDst/4-4            79.0MB/s ± 7%
MemmoveUnalignedDst/5-4            95.3MB/s ± 5%
MemmoveUnalignedDst/6-4             104MB/s ± 7%
MemmoveUnalignedDst/7-4             115MB/s ± 5%
MemmoveUnalignedDst/8-4            11.9MB/s ± 1%
MemmoveUnalignedDst/9-4            13.2MB/s ± 1%
MemmoveUnalignedDst/10-4           14.5MB/s ± 2%
MemmoveUnalignedDst/11-4           16.0MB/s ± 0%
MemmoveUnalignedDst/12-4           17.3MB/s ± 1%
MemmoveUnalignedDst/13-4           18.7MB/s ± 1%
MemmoveUnalignedDst/14-4           20.0MB/s ± 0%
MemmoveUnalignedDst/15-4           21.3MB/s ± 0%
MemmoveUnalignedDst/16-4           12.2MB/s ± 2%
MemmoveUnalignedDst/32-4           12.5MB/s ± 1%
MemmoveUnalignedDst/64-4           12.6MB/s ± 1%
MemmoveUnalignedDst/128-4          12.7MB/s ± 0%
MemmoveUnalignedDst/256-4          12.8MB/s ± 0%
MemmoveUnalignedDst/512-4          12.8MB/s ± 1%
MemmoveUnalignedDst/1024-4         12.8MB/s ± 0%
MemmoveUnalignedDst/2048-4         12.8MB/s ± 1%
MemmoveUnalignedDst/4096-4         12.8MB/s ± 1%
MemmoveUnalignedDstOverlap/32-4    16.2MB/s ± 1%
MemmoveUnalignedDstOverlap/64-4    14.3MB/s ± 0%
MemmoveUnalignedDstOverlap/128-4   13.5MB/s ± 1%
MemmoveUnalignedDstOverlap/256-4   13.2MB/s ± 0%
MemmoveUnalignedDstOverlap/512-4   13.0MB/s ± 0%
MemmoveUnalignedDstOverlap/1024-4  12.9MB/s ± 1%
MemmoveUnalignedDstOverlap/2048-4  12.9MB/s ± 0%
MemmoveUnalignedDstOverlap/4096-4  12.9MB/s ± 0%
MemmoveUnalignedSrc/0-4
MemmoveUnalignedSrc/1-4            30.2MB/s ±10%
MemmoveUnalignedSrc/2-4            54.8MB/s ±15%
MemmoveUnalignedSrc/3-4            66.5MB/s ± 5%
MemmoveUnalignedSrc/4-4            75.5MB/s ± 7%
MemmoveUnalignedSrc/5-4            92.0MB/s ± 6%
MemmoveUnalignedSrc/6-4             100MB/s ± 4%
MemmoveUnalignedSrc/7-4             115MB/s ± 3%
MemmoveUnalignedSrc/8-4             110MB/s ± 4%
MemmoveUnalignedSrc/9-4             114MB/s ± 5%
MemmoveUnalignedSrc/10-4            116MB/s ± 5%
MemmoveUnalignedSrc/11-4            124MB/s ± 4%
MemmoveUnalignedSrc/12-4            127MB/s ± 3%
MemmoveUnalignedSrc/13-4            133MB/s ± 5%
MemmoveUnalignedSrc/14-4            144MB/s ± 4%
MemmoveUnalignedSrc/15-4           21.5MB/s ± 0%
MemmoveUnalignedSrc/16-4           22.4MB/s ± 2%
MemmoveUnalignedSrc/32-4           16.2MB/s ± 1%
MemmoveUnalignedSrc/64-4           14.3MB/s ± 1%
MemmoveUnalignedSrc/128-4          13.6MB/s ± 1%
MemmoveUnalignedSrc/256-4          13.1MB/s ± 1%
MemmoveUnalignedSrc/512-4          13.0MB/s ± 1%
MemmoveUnalignedSrc/1024-4         12.9MB/s ± 1%
MemmoveUnalignedSrc/2048-4         12.8MB/s ± 1%
MemmoveUnalignedSrc/4096-4         12.8MB/s ± 0%
MemmoveUnalignedSrcOverlap/32-4    12.5MB/s ± 0%
MemmoveUnalignedSrcOverlap/64-4    12.7MB/s ± 1%
MemmoveUnalignedSrcOverlap/128-4   12.8MB/s ± 0%
MemmoveUnalignedSrcOverlap/256-4   12.7MB/s ± 1%
MemmoveUnalignedSrcOverlap/512-4   12.8MB/s ± 1%
MemmoveUnalignedSrcOverlap/1024-4  12.8MB/s ± 1%
MemmoveUnalignedSrcOverlap/2048-4  12.8MB/s ± 0%
MemmoveUnalignedSrcOverlap/4096-4  12.8MB/s ± 1%
@mundaym mundaym added the arch-riscv Issues solely affecting the riscv64 architecture. label Sep 8, 2021
@mundaym mundaym added this to the Go1.18 milestone Sep 8, 2021
@mundaym mundaym self-assigned this Sep 8, 2021
@gopherbot
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Change https://golang.org/cl/348393 mentions this issue: runtime: use aligned loads and stores for memmove on riscv64

@mknyszek
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Unfortunately I think this needs to wait for the next release at this point.

@mknyszek mknyszek modified the milestones: Go1.18, Go1.19 Nov 10, 2021
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 7, 2022
@aclements aclements modified the milestones: Go1.19, Go1.20 Jul 12, 2022
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cc @golang/riscv64

@mengzhuo
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cc @golang/riscv64

This CL still in "merge conflicted"

cc @mundaym Could you take a look? Thanks.

@prattmic prattmic moved this to Triage Backlog in Go Compiler / Runtime Jul 25, 2022
@gopherbot
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Change https://go.dev/cl/426256 mentions this issue: runtime: optimise memmove on riscv64

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@mengzhuo, if you'd like to +2 CL 426256, we can probably get the extra +1 quickly and go ahead and land it.

Repository owner moved this from Triage Backlog to Done in Go Compiler / Runtime Nov 18, 2022
@gopherbot gopherbot moved this to Done in Release Blockers Nov 18, 2022
@randall77
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Someone just tripped over this bug over on golang-dev. They are probably using 1.19 and thus didn't pick up the fix for this bug, but worth watching just in case:
https://groups.google.com/g/golang-dev/c/5Om3lJcYxzA/m/UyhzduXTBgAJ?utm_medium=email&utm_source=footer

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Labels
arch-riscv Issues solely affecting the riscv64 architecture. compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge Performance
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Status: Done
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Go1.20
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