Fix querying L3 cache size on osx-x64

[filipnavara]

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
Assignees:	-
Labels:	area-GC-coreclr
Milestone:	-

[EgorBo]

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

[EgorBo]

Thanks!

[filipnavara]

We should probably backport this to release/7.0.

[EgorBo]

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]

is heuristic the same for workstation gc?

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

[EgorBo]

/backport to release/7.0-rc2

[github-actions]

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