linuxppc / linuxppc/issues

Test/enable CPU_MASK_OFFSTACK

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enhancement
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Description

@srikard points out that we never select CPU_MASK_OFFSTACK, even for NR_CPUS=8192.

This probably means a NR_CPUS=8192 config would have issues with stack usage, although possibly we get away with it due to having relatively large THREAD_SHIFT.

We also have a few usages of zalloc_cpumask_var() which lack error checking. With CPU_MASK_OFFSTACK=y they could potentially fail.

We should test that CPU_MASK_OFFSTACK works, and then select it for NR_CPUs above some threshold. Not clear what the threshold should be, would need some performance/memory-usage analysis.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by testing a configuration with NR_CPUS=8192 and CPU_MASK_OFFSTACK enabled, then inspect the zalloc_cpumask_var() usages mentioned in the issue. Done means confirming whether CPU_MASK_OFFSTACK works, identifying a threshold through performance and memory-use analysis, and addressing potential allocation failures.

Written by the indexing model from the issue text.

Assessment

Tech stack
linux
Domain
operating-systems
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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