sdma_map_init(9)

okay bestie, welcome to sdma_map_init(9) from the Kernel API Manual 💖 this is the little routine that changes the mapping based on the number of vls, and we’re gonna get into it. no cap.

✨ NAME ✨

sdma_map_init — called when # vls change 💅

🌸 SYNOPSIS 🌸

int sdma_map_init (struct hfi1_devdata *dd , u8 port , u8 num_vls , u8
*vl_engines );

🎀 ARGUMENTS 🎀

• dd — hfi1_devdata 🫶
• port — port number
• num_vls — number of vls
• vl_engines — per vl engine mapping (optional)

🦋 DESCRIPTION 🦋

okay so this routine changes the mapping based on the number of vls. literally its whole thing.

vl_engines is used to specify a non-uniform vl/engine loading. if it’s NULL, that implies auto computing the loading and giving each VLs a uniform distribution of engines per VL. ✨

the auto algorithm computes the sde_per_vl and the number of extra engines. any extra engines are added from the last VL on down. 👑

rcu locking is used here to control access to the mapping fields. 🔒

if either the num_vls or num_sdma are non-power of 2, the array sizes in the struct sdma_vl_map and the struct sdma_map_elem are rounded up to the next highest power of 2, and the first entry is reused in a round robin fashion. 🌀

if an error occurs, the map change is not done and the mapping is not changed. periodt. 💀

🌈 SEE ALSO 🌈

Kernel file ./drivers/infiniband/hw/hfi1/sdma.c — plus the whole function bestie squad, in order:

• sdma_state_name(9)
• sdma_get_descq_cnt(9)
• sdma_engine_get_vl(9)
• sdma_select_engine_vl(9)
• sdma_select_engine_sc(9)
• sdma_seqfile_dump_cpu_list(9)
• sdma_clean(9)
• sdma_init(9)
• sdma_all_running(9)
• sdma_start(9)
• sdma_exit(9)
• __sdma_txclean(9)
• sdma_engine_error(9)
• sdma_seqfile_dump_sde(9)
• sdma_send_txreq(9)
• sdma_send_txlist(9)
• sdma_ahg_alloc(9)
• sdma_ahg_free(9)
• _sdma_engine_progress_schedule(9)

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mwah 💋 that’s the page, signed off with source/version ./drivers/infiniband/hw/hfi1, date October 2026, and title sdma_map_init(9). 🫶✨