mlx5dv_map_ah_to_qp(3)

📦
version 62.0 · 8 versions
, in alpine 3.24, centos-stream 10, centos-stream 9, ubuntu jammy

💅 mlx5dv_map_ah_to_qp(3) 💅

okay so bestie, welcome to section 3 of the manual — mlx5dv_map_ah_to_qp, the little function that makes your address handle and your QP get along. genuinely iconic behavior, no cap.

✨ NAME ✨

mlx5dv_map_ah_to_qp — maps the destination path information that lives in an address handle (AH) over to the info we pull out of the qp. it's giving matchmaker energy fr fr 🎀

🌸 SYNOPSIS 🌸

#include <infiniband/mlx5dv.h>

int mlx5dv_map_ah_to_qp(struct ibv_ah *ah, uint32_t qp_num);

look at her. two arguments. immaculate. 🫶

🦋 DESCRIPTION 🦋

so what does this API actually do? it maps the destination path information sitting in the address handle (ah) to the information that gets extracted from the qp — think congestion control coming from ECE, iykyk. 💫

this API is literally an enhancement to DC and UD QPs, and the whole point is better performance: it lets you use per-address congestion control (CC) algorithms, which means DC/UD QPs can run multiple CC algorithms inside the same datacenter. main character energy for your fabric, honestly. 🔥

the mapping this API creates is implicitly destroyed when the address handle is destroyed, bestie. that's just how it goes.

and listen — it is not affected by the destruction of QP qp_num. so go ahead and yeet that QP, the mapping stays put. 💀

a duplicate mapping to the same address handle? ignored. because in that case this API is just a hint for the hardware, so it would do nothing and return success regardless of the new qp_num ECE. yes, regardless — that part matters. 🙈

one more thing, and this is the part people miss: the function must be called after ECE negotiation/preconfiguration was done by some external means. don't skip that step, queen. 👑

💖 ARGUMENTS 💖

  • ah — the target's address handle. the destination-vibe holder. 📍
  • qp_num — the initiator QP whose congestion control info gets extracted from its ECE. this is where the CC tea comes from. 🍓

⭐ RETURN VALUE ⭐

  • upon success → returns 0 ✨ slay
  • upon failure → the value of errno is returned 😭

🌈 SEE ALSO 🌈

go read those too, they're all part of the same friend group, fr fr. 🧚

👑 AUTHOR 👑

  • Yochai Cohen <yochai@nvidia.com>
  • Patrisious Haddad <phaddad@nvidia.com>

two legends. we stan. 💜

and that's the whole page!! the header up top says mlx5dv_map_ah_to_qp(3) and the footer at the bottom just repeats mlx5dv_map_ah_to_qp(3) with no fancy source/version or date info attached — so like, no extra lore there, sorry bestie 🎀 mwah, go map some AHs to some QPs, periodt. 💅

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