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github-data/discussions/619 - gpu p2p utilization.md

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+### 🗣️ [#619](https://github.com/ikawrakow/ik_llama.cpp/discussions/619) - gpu p2p utilization
+
+| **Author** | `magikRUKKOLA` |
+| :--- | :--- |
+| **Created** | 2025-07-16 |
+| **Updated** | 2025-07-17 |
+
+---
+
+#### Description
+
+Is there any mode of the llm inference in ik_llama.cpp that utilizes the p2p functionality between the GPUs?  That would include the NVLINKs and, most importantly, the regular p2p master-slave functionality as enabled by the opensource nvidia drivers (see https://github.com/aikitoria/open-gpu-kernel-modules ).
+
+[EDIT]:
+
+with and without p2p functionality:
+
+```bash
+/usr/share/doc/nvidia-cuda-toolkit/examples/Samples/5_Domain_Specific/p2pBandwidthLatencyTest/p2pBandwidthLatencyTest
+
+Bidirectional P2P=Disabled Bandwidth Matrix (GB/s)
+   D\D     0      1      2
+     0 839.83  14.54  16.64
+     1  14.53 839.83  16.67
+     2  16.72  16.67 840.26
+Bidirectional P2P=Enabled Bandwidth Matrix (GB/s)
+   D\D     0      1      2
+     0 839.15  52.04  52.04
+     1  52.04 839.83  52.03
+     2  51.94  52.03 839.83
+```
+
+So there is about 35 GB/s free bandwidth available for the nvidia gpu users.
+
+[EDIT]:
+If I am reading the code correctly, the p2p functionality is used only at: ggml_backend_sycl_graph_compute and the ggml_sycl_set_peer_access is allowing it only if n_tokens is less than 128?  Can anyone provide more info?
+
+[EDIT2]:
+Uh oh?
+
+```
+4415 //todo, it's known issue：error in device2device cross GPUs. reused when the issue is fixed. DON"T remove
+4416 #if 0
+4417         SYCL_CHECK(CHECK_TRY_ERROR((*stream).memcpy(
+4418             (char *)dst->data, (const char *)src->data, size).wait()));
+4419
+4420         /*
+4421         DPCT1009:201: SYCL uses exceptions to report errors and does not use the
+4422         error codes. The original code was commented out and a warning string
+4423         was inserted. You need to rewrite this code.
+4424         */
+4425         SYCL_CHECK(CHECK_TRY_ERROR(
+4426             dpct::dev_mgr::instance().get_device(dst_ctx->device).queues_wait_and_throw()));
+4427 #endif
+```