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Fix querying L3 cache size on osx-x64 - #75854

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EgorBo merged 1 commit into
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filipnavara:l3-size-os-x64
Sep 20, 2022
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Fix querying L3 cache size on osx-x64#75854
EgorBo merged 1 commit into
dotnet:mainfrom
filipnavara:l3-size-os-x64

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@filipnavara

@filipnavarafilipnavara commented Sep 19, 2022•
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Originally reported here:

The code for determining the L3 cache size returns incorrect value on osx-x64. The machine I use for testing is running macOS 12.2.1 on Intel i5-8500B processor. This processor has 9MB of L3 cache but only 256Kb of L2 cache. The ARM64 fix for checking hw.perflevel0.l2cachesize mistakenly returns the L2 cache size on this machine. This in turn results in abysmal GC performance (on debug builds, at least) and frequent garbage collections.

Values on Intel:

teamcity@172-4-1-71 runtime % sysctl hw.perflevel0.l2cachesize
hw.perflevel0.l2cachesize: 262144
teamcity@172-4-1-71 runtime % sysctl hw.perflevel0.l3cachesize
hw.perflevel0.l3cachesize: 9437184
teamcity@172-4-1-71 runtime % sysctl hw.l3cachesize hw.l3cachesize: 9437184

Values on M1:

filipnavara@172-4-1-20 runtime % sysctl hw.perflevel0.l2cachesize
hw.perflevel0.l2cachesize: 12582912
filipnavara@172-4-1-20 runtime % sysctl hw.perflevel0.l3cachesize
filipnavara@172-4-1-20 runtime % sysctl hw.l3cachesize

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Issue Details

Originally reported here:

The code for determining the L3 cache size returns incorrect value on osx-x64. The machine I use for testing is running macOS 12.2.1 on Intel i5-8500B processor. This processor has 9MB of L3 cache but only 256Kb of L2 cache. The ARM64 fix for checking hw.perflevel0.l2cachesize mistakenly returns the L2 cache size on this machine. This in turn results in abysmal GC performance and frequent garbage collections.

Values on Intel:

teamcity@172-4-1-71 runtime % sysctl hw.perflevel0.l2cachesize
hw.perflevel0.l2cachesize: 262144
teamcity@172-4-1-71 runtime % sysctl hw.perflevel0.l3cachesize
hw.perflevel0.l3cachesize: 9437184
teamcity@172-4-1-71 runtime % sysctl hw.l3cachesize hw.l3cachesize: 9437184

Values on M1:

filipnavara@172-4-1-20 runtime % sysctl hw.perflevel0.l2cachesize
hw.perflevel0.l2cachesize: 12582912
filipnavara@172-4-1-20 runtime % sysctl hw.perflevel0.l3cachesize
filipnavara@172-4-1-20 runtime % sysctl hw.l3cachesize
Author:filipnavara
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EgorBo
EgorBo reviewed Sep 19, 2022
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Comment threadsrc/coreclr/gc/unix/gcenv.unix.cpp
// macOS-arm64: Since macOS 12.0, Apple added ".perflevelX." to determinate cache sizes for efficiency
// macOS: Since macOS 12.0, Apple added ".perflevelX." to determinate cache sizes for efficiency
// and performance cores separately. "perflevel0" stands for "performance"
|| sysctlbyname("hw.perflevel0.l3cachesize", &cacheSizeFromSysctl, &sz, nullptr, 0) == 0

@EgorBoEgorBoSep 19, 2022

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Ah, I didn't add it because it wasn't used on arm64 🙂

EgorBo
EgorBo approved these changes Sep 19, 2022
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Thanks!

@filipnavara

filipnavara commented Sep 19, 2022

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We should probably backport this to release/7.0.

@filipnavarafilipnavara mentioned this pull request Sep 19, 2022
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@EgorBo
EgorBo merged commit 7dad0f3 into dotnet:mainSep 20, 2022
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EgorBo commented Sep 20, 2022

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We should probably backport this to release/7.0.

Probably indeed makes sense as 256kb is quite small for gen0 budget (is heuristic the same for workstation gc?)
and might hurt VSfM/Rider/etc apps (unlikely anyone is hosting web services on mac, right?)

@filipnavara

filipnavara commented Sep 20, 2022

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is heuristic the same for workstation gc?

Yep, I hit it on workstation GC in the first place.

@EgorBo

EgorBo commented Sep 20, 2022

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/backport to release/7.0-rc2

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github-actionsBot commented Sep 20, 2022

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Started backporting to release/7.0-rc2: https://github.com/dotnet/runtime/actions/runs/3086969575

@github-actionsgithub-actionsBot mentioned this pull request Sep 20, 2022
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@filipnavarafilipnavara mentioned this pull request Sep 29, 2022
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@filipnavara
filipnavara deleted the l3-size-os-x64 branch June 5, 2025 07:48
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@EgorBoEgorBoEgorBo approved these changes
@jkotasjkotasjkotas approved these changes
@janvorlijanvorliAwaiting requested review from janvorli

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