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Use sync regs instead of get/set regs on KVM #200

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Enhancement
Closed
Use sync regs instead of get/set regs on KVM#200
Enhancement
Labels
area/performanceAddresses performancelifecycle/confirmedBug is verified or proposal seems reasonable
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Upcoming

Description

@simongdavies
simongdavies
opened on Jan 29, 2025

KVM has a set of functions (sync_regs, sync_regs_mut, clear_sync_dirty_regs, clear_sync_valid_regs, set_sync_dirty_regs and set_sync_valid_regs) that cause synchronisation of registers without the need to call get/set regs, this improves performance as it means that extra ioctls are not required to retrieve or set registers.

We should replace get/set regs with the appropriate sync functions

Activity

  1. simongdavies
    added
    kind/enhancementFor PRs adding features, improving functionality, docs, tests, etc.
    on Jan 29, 2025
  2. github-actions
    added
    lifecycle/needs-reviewThe issue has not yet been reviewed.
    on Jan 29, 2025
  3. syntactically
    added
    area/performanceAddresses performance
    and removed
    kind/enhancementFor PRs adding features, improving functionality, docs, tests, etc.
    on Feb 5, 2025
  4. danbugs
    added this to Hyperlight Milestoneson Mar 4, 2025
  5. danbugs
    added this to the Backlog milestone on Mar 4, 2025

  6. danbugs commented on Mar 26, 2025

    @danbugs
    danbugs
    on Mar 26, 2025
    Contributor

    MSHV has an equivalent API for this too now.

  7. danbugs
    modified the milestones: Backlog, Upcoming on Mar 26, 2025
  8. danbugs
    added
    lifecycle/confirmedBug is verified or proposal seems reasonable
    and removed
    lifecycle/needs-reviewThe issue has not yet been reviewed.
    on Mar 26, 2025

  9. syntactically commented on Mar 27, 2025

    @syntactically
    syntactically
    on Mar 27, 2025
    Member

    MSHV has an equivalent API for this too now.

    IIRC most of the MSHV exit types also copy the registers into userspace as part of the HV exit message, so we don't even need an ioctl at all in some cases.

  10. ludfjig commented on Sep 22, 2026

    @ludfjig
    ludfjig
    on Sep 22, 2026
    Contributor

    I implemented this and compared to main using guest_calls/call/* benchmarks, but showed no perf improvement whatsoever. Closing this for now

  11. ludfjig
    closed this as completedon Sep 22, 2026
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