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Respect environment variables for disabling Vector support #84461

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jeffhandley opened this issue Apr 7, 2023 · 2 comments
Closed

Respect environment variables for disabling Vector support #84461

jeffhandley opened this issue Apr 7, 2023 · 2 comments
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@tannergooding
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area-System.Runtime.Intrinsics
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8.0.0

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@jeffhandley
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As was metnioned in #84115 (comment)_, it would be relatively simple to recognize environment variables for disabling vector support--especially to help with testing.

Today, setting DOTNET_EnableAVX2=0 results in Vector256.IsHardwareAccelerated returning false and setting DOTNET_EnableHWIntrinsic=0 will result in Vector64.IsHardwareAccelerated and Vector.IsHardwareAccelerated returning false.

Instead of requiring those two environment variables to be set and used in different test runs, we could respect DOTNET_EnableVector128 and probably several others. This approach would make the test scenarios easier to reason about..
@dotnet-issue-labeler dotnet-issue-labeler bot added the needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners label Apr 7, 2023
@ghost ghost added the untriaged New issue has not been triaged by the area owner label Apr 7, 2023
@jeffhandley jeffhandley added area-System.Runtime.Intrinsics and removed needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners labels Apr 7, 2023
@jeffhandley jeffhandley added this to the 8.0.0 milestone Apr 7, 2023
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ghost commented Apr 7, 2023

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Issue Details

As was metnioned in #84115 (comment)_, it would be relatively simple to recognize environment variables for disabling vector support--especially to help with testing.

Today, setting DOTNET_EnableAVX2=0 results in Vector256.IsHardwareAccelerated returning false and setting DOTNET_EnableHWIntrinsic=0 will result in Vector64.IsHardwareAccelerated and Vector.IsHardwareAccelerated returning false.

Instead of requiring those two environment variables to be set and used in different test runs, we could respect DOTNET_EnableVector128 and probably several others. This approach would make the test scenarios easier to reason about..

Author: jeffhandley
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area-System.Runtime.Intrinsics, untriaged
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@ghost ghost removed the untriaged New issue has not been triaged by the area owner label Apr 7, 2023
@jeffhandley jeffhandley mentioned this issue Jun 28, 2023
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@tannergooding
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There is a better way to control this via the DOTNET_MaxVectorTBitWidth property that impacts the size of Vector<T>.

There also exists an undocumented DOTNET_PreferredVectorBitWidth that impacts whether Vector256/512.IsHardwareAccelerated report true.

Vector128 and Vector<T> themselves are "core" types for many platforms and DOTNET_EnableHWIntrinsic is the only way to disable them by design.

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