https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230334
Bug ID: 230334
Summary: busdma(9) is missing bus_dmamap_sync_range()
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Some People
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: jhibb...@freebsd.org
bus_dmamap_sync(9) syncs the entire page range in a mapping, which can be very
costly if only a small range is needed.
Some drivers, perhaps many, share DMA maps for multiple queues or entries, and
only need to update one segment. Instead of syncing the full map, there should
be a way to sync only the updated range.
This is mentioned in https://reviews.freebsd.org/D16570 regarding NVMe
performance implications, and in https://reviews.freebsd.org/D16517 as missing
for sound buffers.
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