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x86/iommu: Reduce the number of queued invalidation interrupts

Authored by alc on Aug 6 2022, 7:36 AM.



Restructure dmar_qi_task() so as to reduce the number of invalidation completion interrupts. Specifically, because processing completed invalidations in dmar_qi_task() can take some time, don't reenable completion interrupts until we have finished processing the completed invalidations a first time. Then, check a second time after reenabling completion interrupts, so that invalidations that completed just before interrupts were reenabled do not linger until a future invalidation raises an interrupt. Testing for completed invalidations is now cheap; no locking is required.

Test Plan
netperf -H lip3 -t TCP_MAERTS -i 20


irq25: dmar0:qi                 35094545     144718


irq25: dmar0:qi                 28855066      92485

Diff Detail

rG FreeBSD src repository
Automatic diff as part of commit; lint not applicable.
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

alc requested review of this revision.Aug 6 2022, 7:36 AM
alc created this revision.
This revision is now accepted and ready to land.Aug 6 2022, 1:13 PM