Use atomic load and stores to ensure that the compiler doesn't optimize away these loops.
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Authored by imp on Jan 25 2018, 10:17 PM.

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Reviewers

kib
scottl
jimharris

Commits

rS328521: Use atomic load and stores to ensure that the compiler doesn't

Summary

Use atomic load and stores to ensure that the compiler doesn't optimize away these loops. Change boolean to int to match what atomic API supplies. Remove wmb() since the atomic_store_rel() on status.done ensure the prior writes to status.

Coverity caught this, and kib@ suggested these changes. They supposedly also use fewer cycles.

Test Plan

Booted on two different machines.

Diff Detail

Repository

rS FreeBSD src repository - subversion

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Event Timeline

imp created this revision.Jan 25 2018, 10:17 PM

Harbormaster completed remote builds in B14582: Diff 38462.Jan 25 2018, 10:17 PM

imp retitled this revision from Use atomic load and stores to ensure that the compiler doesn't optimize away these loops. Change boolean to int to match what atomic API supplies. Remove wmb() since the atomic_store_rel() on status.done ensure the prior writes to status. to Use atomic load and stores to ensure that the compiler doesn't optimize away these loops..Jan 25 2018, 10:19 PM

imp edited the summary of this revision. (Show Details)

imp added reviewers: kib, scottl, jimharris.

This also fixes a bug that rmb() was missed between read of status.done and accessing the controller data.

This revision is now accepted and ready to land.Jan 25 2018, 10:27 PM

scottl accepted this revision.Jan 25 2018, 10:37 PM

imp edited the test plan for this revision. (Show Details)Jan 25 2018, 10:43 PM

jimharris accepted this revision.Jan 27 2018, 4:56 PM

Closed by commit rS328521: Use atomic load and stores to ensure that the compiler doesn't (authored by imp). · Explain WhyJan 29 2018, 12:01 AM

This revision was automatically updated to reflect the committed changes.