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cmd/compile: performance regression compiling crypto/internal/edwards25519/field.feMulGeneric on PPC64 #56497

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pmur opened this issue Oct 31, 2022 · 2 comments
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arch-ppc64x compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge
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@pmur
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pmur commented Oct 31, 2022

The change to support carry flag optimization on ARM64 (go.dev/cl/432275) caused a large regression in the crypto/ed25519 benchmarks. I missed this regression when reviewing the patch.

The optimization created by using the CarryChainTail priority fails when schedulable memory ops get intertwined with schedulable CarryChainTail ops like ADDZ on PPC64. This leads to many avoidable CA bit clobbers.

What did you expect to see?

No difference in benchmark tests.

What did you see instead?

name              old time/op  new time/op  delta
KeyGeneration-2   27.2µs ± 0%  29.6µs ± 0%   +9.05%  (p=1.000 n=1+1)
NewKeyFromSeed-2  23.9µs ± 0%  29.4µs ± 0%  +23.13%  (p=1.000 n=1+1)
Signing-2         33.7µs ± 0%  37.2µs ± 0%  +10.36%  (p=1.000 n=1+1)
Verification-2    68.3µs ± 0%  88.8µs ± 0%  +30.06%  (p=1.000 n=1+1)
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Oct 31, 2022
@pmur pmur changed the title cmd/compile: performance regression compiling crypto/internal/edwards25519/field.feMulGeneric cmd/compile: performance regression compiling crypto/internal/edwards25519/field.feMulGeneric on PPC64 Oct 31, 2022
@mknyszek
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mknyszek commented Nov 2, 2022

In triage, context from @cherrymui, @pmur is already looking into it so assigning it to you.

@mknyszek mknyszek modified the milestones: Backlog, Go1.20 Nov 2, 2022
@gopherbot
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Change https://go.dev/cl/447435 mentions this issue: cmd/compile/internal/ssa: re-adjust CarryChainTail priority

@golang golang locked and limited conversation to collaborators Nov 3, 2023
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