Add functions that are used to query Hardware topology.

Change-Id: I0f4cd02b237bde4d6dccfb0e83e65376ecb1cfaa
Signed-off-by: Mike Li <Tianxinmike.Li@amd.com>


[ROCm/amdsmi commit: c7d349183a]

projects/amdsmi/src/rocm_smi.cc

@@ -70,6 +70,7 @@
 #include "rocm_smi/rocm_smi_exception.h"
 #include "rocm_smi/rocm_smi_counters.h"
 #include "rocm_smi/rocm_smi_kfd.h"
+#include "rocm_smi/rocm_smi_io_link.h"
 
 #include "rocm_smi/rocm_smi64Config.h"
 
@@ -1241,6 +1242,30 @@ static rsmi_status_t set_power_profile(uint32_t dv_ind,
   CATCH
 }
 
+static rsmi_status_t topo_get_numa_node_number(uint32_t dv_ind,
+                     uint32_t *numa_node_number) {
+  TRY
+
+  GET_DEV_AND_KFDNODE_FROM_INDX
+
+  *numa_node_number = kfd_node->numa_node_number();
+
+  return RSMI_STATUS_SUCCESS;
+  CATCH
+}
+
+static rsmi_status_t topo_get_numa_node_weight(uint32_t dv_ind,
+                     uint64_t *weight) {
+  TRY
+
+  GET_DEV_AND_KFDNODE_FROM_INDX
+
+  *weight = kfd_node->numa_node_weight();
+
+  return RSMI_STATUS_SUCCESS;
+  CATCH
+}
+
 rsmi_status_t
 rsmi_dev_gpu_clk_freq_get(uint32_t dv_ind, rsmi_clk_type_t clk_type,
                                                         rsmi_frequencies_t *f) {
@@ -2964,6 +2989,158 @@ rsmi_dev_xgmi_error_reset(uint32_t dv_ind) {
   CATCH
 }
 
+rsmi_status_t
+rsmi_topo_get_numa_node_number(uint32_t dv_ind, uint32_t *numa_node) {
+  TRY
+
+  return topo_get_numa_node_number(dv_ind, numa_node);
+  CATCH
+}
+
+rsmi_status_t
+rsmi_topo_get_link_weight(uint32_t dv_ind_src, uint32_t dv_ind_dst,
+                          uint64_t *weight) {
+  TRY
+
+  uint32_t dv_ind = dv_ind_src;
+  GET_DEV_AND_KFDNODE_FROM_INDX
+  DEVICE_MUTEX
+
+  if (weight == nullptr) {
+    return RSMI_STATUS_INVALID_ARGS;
+  }
+
+  rsmi_status_t status;
+  uint32_t node_ind_dst;
+  uint32_t ret = smi.get_node_index(dv_ind_dst, &node_ind_dst);
+
+  if (!ret) {
+    amd::smi::IO_LINK_TYPE type;
+    ret = kfd_node->get_io_link_type(node_ind_dst, &type);
+    if (!ret) {
+      if (type == amd::smi::IOLINK_TYPE_XGMI) {
+        ret = kfd_node->get_io_link_weight(node_ind_dst, weight);
+        if (!ret)
+          status = RSMI_STATUS_SUCCESS;
+        else
+          status = RSMI_STATUS_INIT_ERROR;
+      } else {
+        assert(!"Unexpected IO Link type read");
+        status = RSMI_STATUS_NOT_SUPPORTED;
+      }
+    } else {
+      *weight = kfd_node->numa_node_weight();  // from src GPU to it's CPU node
+      uint64_t numa_weight_dst;
+      status = topo_get_numa_node_weight(dv_ind_dst, &numa_weight_dst);
+      // from dst GPU to it's CPU node
+      if (status == RSMI_STATUS_SUCCESS) {
+        *weight = *weight + numa_weight_dst;
+        uint32_t numa_number_src = kfd_node->numa_node_number();
+        uint32_t numa_number_dst;
+        status = topo_get_numa_node_number(dv_ind_dst, &numa_number_dst);
+        if (status == RSMI_STATUS_SUCCESS) {
+          if (numa_number_src != numa_number_dst) {
+            uint64_t io_link_weight;
+            ret = smi.get_io_link_weight(numa_number_src, numa_number_dst,
+                                         &io_link_weight);
+            if (!ret) {
+              *weight = *weight + io_link_weight;
+              // from src numa CPU node to dst numa CPU node
+            } else {
+              *weight = *weight + 10;
+              // More than one CPU hops, hard coded 10
+            }
+          }
+          status = RSMI_STATUS_SUCCESS;
+        } else {
+          assert(!"Error to read numa node number");
+          status = RSMI_STATUS_INIT_ERROR;
+        }
+      } else {
+        assert(!"Error to read numa node weight");
+        status = RSMI_STATUS_INIT_ERROR;
+      }
+    }
+  } else {
+    status = RSMI_STATUS_INVALID_ARGS;
+  }
+
+  return status;
+  CATCH
+}
+
+rsmi_status_t
+rsmi_topo_get_link_type(uint32_t dv_ind_src, uint32_t dv_ind_dst,
+                        uint64_t *hops, RSMI_IO_LINK_TYPE *type) {
+  TRY
+
+  uint32_t dv_ind = dv_ind_src;
+  GET_DEV_AND_KFDNODE_FROM_INDX
+
+  if (hops == nullptr) {
+    return RSMI_STATUS_INVALID_ARGS;
+  }
+
+  if (type == nullptr) {
+    return RSMI_STATUS_INVALID_ARGS;
+  }
+
+  rsmi_status_t status;
+  uint32_t node_ind_dst;
+  uint32_t ret = smi.get_node_index(dv_ind_dst, &node_ind_dst);
+
+  if (!ret) {
+    amd::smi::IO_LINK_TYPE io_link_type;
+    ret = kfd_node->get_io_link_type(node_ind_dst, &io_link_type);
+    if (!ret) {
+      if (io_link_type == amd::smi::IOLINK_TYPE_XGMI) {
+        *type = RSMI_IOLINK_TYPE_XGMI;
+        *hops = 1;
+        status = RSMI_STATUS_SUCCESS;
+      } else {
+        assert(!"Unexpected IO Link type read");
+        status = RSMI_STATUS_NOT_SUPPORTED;
+      }
+    } else {
+      uint32_t numa_number_dst;
+      status = topo_get_numa_node_number(dv_ind_dst, &numa_number_dst);
+      if (status == RSMI_STATUS_SUCCESS) {
+        uint32_t numa_number_src = kfd_node->numa_node_number();
+        if (numa_number_src == numa_number_dst) {
+          *hops = 2;  // same CPU node
+        } else {
+          uint64_t io_link_weight;
+          ret = smi.get_io_link_weight(numa_number_src, numa_number_dst,
+                                       &io_link_weight);
+          if (!ret)
+            *hops = 3;  // from src CPU node to dst CPU node
+          else
+            *hops = 4;  // More than one CPU hops, hard coded as 4
+        }
+
+        amd::smi::IO_LINK_TYPE numa_node_type = kfd_node->numa_node_type();
+        if (numa_node_type == amd::smi::IOLINK_TYPE_PCIEXPRESS) {
+          *type = RSMI_IOLINK_TYPE_PCIEXPRESS;
+          status = RSMI_STATUS_SUCCESS;
+        } else if (numa_node_type == amd::smi::IOLINK_TYPE_XGMI) {
+          *type = RSMI_IOLINK_TYPE_XGMI;
+          status = RSMI_STATUS_SUCCESS;
+        } else {
+          status = RSMI_STATUS_INIT_ERROR;
+        }
+      } else {
+        assert(!"Error to get numa node number");
+        status = RSMI_STATUS_INIT_ERROR;
+      }
+    }
+  } else {
+    status = RSMI_STATUS_INVALID_ARGS;
+  }
+
+  return status;
+  CATCH
+}
+
 enum iterator_handle_type {
   FUNC_ITER = 0,
   VARIANT_ITER,

projects/amdsmi/src/rocm_smi_io_link.cc

@@ -0,0 +1,356 @@
+/*
+ * =============================================================================
+ * The University of Illinois/NCSA
+ * Open Source License (NCSA)
+ *
+ * Copyright (c) 2020, Advanced Micro Devices, Inc.
+ * All rights reserved.
+ *
+ * Developed by:
+ *
+ *                 AMD Research and AMD ROC Software Development
+ *
+ *                 Advanced Micro Devices, Inc.
+ *
+ *                 www.amd.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal with the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ *  - Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimers.
+ *  - Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimers in
+ *    the documentation and/or other materials provided with the distribution.
+ *  - Neither the names of <Name of Development Group, Name of Institution>,
+ *    nor the names of its contributors may be used to endorse or promote
+ *    products derived from this Software without specific prior written
+ *    permission.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS WITH THE SOFTWARE.
+ *
+ */
+
+#include <assert.h>
+#include <sys/stat.h>
+#include <dirent.h>
+
+#include <algorithm>
+#include <string>
+#include <unordered_set>
+#include <fstream>
+#include <cstdint>
+#include <iostream>
+#include <sstream>
+
+#include "rocm_smi/rocm_smi.h"
+#include "rocm_smi/rocm_smi_exception.h"
+#include "rocm_smi/rocm_smi_utils.h"
+#include "rocm_smi/rocm_smi_io_link.h"
+
+namespace amd {
+namespace smi {
+
+static const char *kKFDNodesPathRoot = "/sys/class/kfd/kfd/topology/nodes";
+
+// IO Link Property strings
+static const char *kIOLinkPropTYPEStr =  "type";
+// static const char *kIOLinkPropVERSION_MAJORStr = "version_major";
+// static const char *kIOLinkPropVERSION_MINORStr = "version_minor";
+static const char *kIOLinkPropNODE_FROMStr = "node_from";
+static const char *kIOLinkPropNODE_TOStr = "node_to";
+static const char *kIOLinkPropWEIGHTStr = "weight";
+// static const char *kIOLinkPropMIN_LATENCYStr = "min_latency";
+// static const char *kIOLinkPropMAX_LATENCYStr = "max_latency";
+// static const char *kIOLinkPropMIN_BANDWIDTHStr = "min_bandwidth";
+// static const char *kIOLinkPropMAX_BANDWIDTHStr = "max_bandwidth";
+// static const char *kIOLinkPropRECOMMENDED_TRANSFER_SIZEStr =
+// "recommended_transfer_size";
+// static const char *kIOLinkPropFLAGSStr = "flags";
+
+static bool is_number(const std::string &s) {
+  return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);
+}
+
+static std::string IOLinkPathRoot(uint32_t node_indx) {
+  std::string io_link_path = kKFDNodesPathRoot;
+  io_link_path += '/';
+  io_link_path += std::to_string(node_indx);
+  io_link_path += '/';
+  io_link_path += "io_links";
+  return io_link_path;
+}
+
+static std::string IOLinkPath(uint32_t node_indx, uint32_t link_indx) {
+  std::string io_link_path = IOLinkPathRoot(node_indx);
+  io_link_path += '/';
+  io_link_path += std::to_string(link_indx);
+  return io_link_path;
+}
+
+static int OpenIOLinkProperties(uint32_t node_indx, uint32_t link_indx,
+                                std::ifstream *fs) {
+  int ret;
+  std::string f_path;
+  bool reg_file;
+
+  assert(fs != nullptr);
+  if (fs == nullptr) {
+    return EINVAL;
+  }
+
+  f_path = IOLinkPath(node_indx, link_indx);
+  f_path += "/";
+  f_path += "properties";
+
+  ret = isRegularFile(f_path, &reg_file);
+
+  if (ret != 0) {
+    return ret;
+  }
+  if (!reg_file) {
+    return ENOENT;
+  }
+
+  fs->open(f_path);
+
+  if (!fs->is_open()) {
+    return errno;
+  }
+
+  return 0;
+}
+
+static int ReadIOLinkProperties(uint32_t node_indx, uint32_t link_indx,
+                                std::vector<std::string> *retVec) {
+  std::string line;
+  int ret;
+  std::ifstream fs;
+
+  assert(retVec != nullptr);
+  if (retVec == nullptr) {
+    return EINVAL;
+  }
+
+  ret = OpenIOLinkProperties(node_indx, link_indx, &fs);
+
+  if (ret) {
+    return ret;
+  }
+
+  while (std::getline(fs, line)) {
+    retVec->push_back(line);
+  }
+
+  if (retVec->size() == 0) {
+    fs.close();
+    return 0;
+  }
+
+  // Remove any *trailing* empty (whitespace) lines
+  while (retVec->back().find_first_not_of(" \t\n\v\f\r") == std::string::npos) {
+    retVec->pop_back();
+  }
+
+  fs.close();
+  return 0;
+}
+
+int DiscoverIOLinks(std::map<std::pair<uint32_t, uint32_t>,
+                    std::shared_ptr<IOLink>> *links) {
+  assert(links != nullptr);
+  if (links == nullptr) {
+    return EINVAL;
+  }
+  assert(links->size() == 0);
+
+  links->clear();
+
+  auto kfd_node_dir = opendir(kKFDNodesPathRoot);
+  assert(kfd_node_dir != nullptr);
+
+  auto dentry_kfd = readdir(kfd_node_dir);
+  while (dentry_kfd != nullptr) {
+    if (dentry_kfd->d_name[0] == '.') {
+      dentry_kfd = readdir(kfd_node_dir);
+      continue;
+    }
+
+    if (!is_number(dentry_kfd->d_name)) {
+      dentry_kfd = readdir(kfd_node_dir);
+      continue;
+    }
+
+    uint32_t node_indx = std::stoi(dentry_kfd->d_name);
+    std::shared_ptr<IOLink> link;
+    uint32_t link_indx;
+    std::string io_link_path_root = IOLinkPathRoot(node_indx);
+
+    auto io_link_dir = opendir(io_link_path_root.c_str());
+    assert(io_link_dir != nullptr);
+
+    auto dentry_io_link = readdir(io_link_dir);
+    while (dentry_io_link != nullptr) {
+      if (dentry_io_link->d_name[0] == '.') {
+        dentry_io_link = readdir(io_link_dir);
+        continue;
+      }
+
+      if (!is_number(dentry_io_link->d_name)) {
+        dentry_io_link = readdir(io_link_dir);
+        continue;
+      }
+
+      link_indx = std::stoi(dentry_io_link->d_name);
+      link = std::shared_ptr<IOLink>(new IOLink(node_indx, link_indx));
+
+      link->Initialize();
+
+      (*links)[std::make_pair(link->node_from(), link->node_to())] = link;
+
+      dentry_io_link = readdir(io_link_dir);
+    }
+
+    if (closedir(io_link_dir)) {
+      return 1;
+    }
+
+    dentry_kfd = readdir(kfd_node_dir);
+  }
+
+  if (closedir(kfd_node_dir)) {
+    return 1;
+  }
+  return 0;
+}
+
+int DiscoverIOLinksPerNode(uint32_t node_indx, std::map<uint32_t,
+                           std::shared_ptr<IOLink>> *links) {
+  assert(links != nullptr);
+  if (links == nullptr) {
+    return EINVAL;
+  }
+  assert(links->size() == 0);
+
+  links->clear();
+
+  std::shared_ptr<IOLink> link;
+  uint32_t link_indx;
+  std::string io_link_path_root = IOLinkPathRoot(node_indx);
+
+  auto io_link_dir = opendir(io_link_path_root.c_str());
+  assert(io_link_dir != nullptr);
+
+  auto dentry = readdir(io_link_dir);
+  while (dentry != nullptr) {
+    if (dentry->d_name[0] == '.') {
+      dentry = readdir(io_link_dir);
+      continue;
+    }
+
+    if (!is_number(dentry->d_name)) {
+      dentry = readdir(io_link_dir);
+      continue;
+    }
+
+    link_indx = std::stoi(dentry->d_name);
+    link = std::shared_ptr<IOLink>(new IOLink(node_indx, link_indx));
+
+    link->Initialize();
+
+    (*links)[link->node_to()] = link;
+
+    dentry = readdir(io_link_dir);
+  }
+
+  if (closedir(io_link_dir)) {
+    return 1;
+  }
+  return 0;
+}
+
+IOLink::~IOLink() {
+}
+
+int IOLink::ReadProperties(void) {
+  int ret;
+
+  std::vector<std::string> propVec;
+
+  assert(properties_.size() == 0);
+  if (properties_.size() > 0) {
+    return 0;
+  }
+
+  ret = ReadIOLinkProperties(node_indx_, link_indx_, &propVec);
+
+  if (ret) {
+    return ret;
+  }
+
+  std::string key_str;
+  uint64_t val_int;  // Assume all properties are unsigned integers for now
+  std::istringstream fs;
+
+  for (uint32_t i = 0; i < propVec.size(); ++i) {
+    fs.str(propVec[i]);
+    fs >> key_str;
+    fs >> val_int;
+
+    properties_[key_str] = val_int;
+
+    fs.str("");
+    fs.clear();
+  }
+
+  return 0;
+}
+
+int
+IOLink::Initialize(void) {
+  int ret = 0;
+  ret = ReadProperties();
+  if (ret) {return ret;}
+
+  ret = get_property_value(kIOLinkPropTYPEStr,
+                           reinterpret_cast<uint64_t *>(&type_));
+  if (ret) {return ret;}
+
+  ret = get_property_value(kIOLinkPropNODE_FROMStr,
+                           reinterpret_cast<uint64_t *>(&node_from_));
+  if (ret) {return ret;}
+
+  ret = get_property_value(kIOLinkPropNODE_TOStr,
+                           reinterpret_cast<uint64_t *>(&node_to_));
+  if (ret) {return ret;}
+
+  ret = get_property_value(kIOLinkPropWEIGHTStr, &weight_);
+
+  return ret;
+}
+
+int
+IOLink::get_property_value(std::string property, uint64_t *value) {
+  assert(value != nullptr);
+  if (value == nullptr) {
+    return EINVAL;
+  }
+  if (properties_.find(property) == properties_.end()) {
+    return EINVAL;
+  }
+  *value = properties_[property];
+  return 0;
+}
+
+}  // namespace smi
+}  // namespace amd

projects/amdsmi/src/rocm_smi_kfd.cc

@@ -53,6 +53,7 @@
 #include <iostream>
 #include <sstream>
 
+#include "rocm_smi/rocm_smi_io_link.h"
 #include "rocm_smi/rocm_smi_kfd.h"
 #include "rocm_smi/rocm_smi.h"
 #include "rocm_smi/rocm_smi_exception.h"
@@ -531,12 +532,49 @@ KFDNode::Initialize(void) {
   if (ret) {return ret;}
 
   ret = ReadKFDGpuId(node_indx_, &gpu_id_);
-  if (ret) {return ret;}
+  if (ret || (gpu_id_ == 0)) {return ret;}
 
   ret = ReadKFDGpuName(node_indx_, &name_);
 
+  std::map<uint32_t, std::shared_ptr<IOLink>> io_link_map_tmp;
+  ret = DiscoverIOLinksPerNode(node_indx_, &io_link_map_tmp);
+  if (ret != 0) {
+    throw amd::smi::rsmi_exception(RSMI_INITIALIZATION_ERROR,
+    "Failed to initialize rocm_smi library (IO Links discovery per node).");
+  }
+
+  std::map<uint32_t, std::shared_ptr<IOLink>>::iterator it;
+  uint32_t node_to;
+  uint64_t node_to_gpu_id;
+  std::shared_ptr<IOLink> link;
+  bool numa_node_found = false;
+  for (it = io_link_map_tmp.begin(); it != io_link_map_tmp.end(); it++) {
+    io_link_map_[it->first] = it->second;
+    node_to = it->first;
+    link = it->second;
+    ret = ReadKFDGpuId(node_to, &node_to_gpu_id);
+    if (ret) {return ret;}
+    if (node_to_gpu_id == 0) {  //  CPU node
+      if (numa_node_found) {
+        if (numa_node_weight_ > link->weight()) {
+          numa_node_number_ = node_to;
+          numa_node_weight_ = link->weight();
+          numa_node_type_ = link->type();
+        }
+      } else {
+        numa_node_number_ = node_to;
+        numa_node_weight_ = link->weight();
+        numa_node_type_ = link->type();
+        numa_node_found = true;
+      }
+    } else {
+      io_link_type_[node_to] = link->type();
+      io_link_weight_[node_to] = link->weight();
+    }
+  }
   return ret;
 }
+
 int
 KFDNode::get_property_value(std::string property, uint64_t *value) {
   assert(value != nullptr);
@@ -550,5 +588,31 @@ KFDNode::get_property_value(std::string property, uint64_t *value) {
   return 0;
 }
 
+int
+KFDNode::get_io_link_type(uint32_t node_to, IO_LINK_TYPE *type) {
+  assert(type != nullptr);
+  if (type == nullptr) {
+    return EINVAL;
+  }
+  if (io_link_type_.find(node_to) == io_link_type_.end()) {
+    return EINVAL;
+  }
+  *type = io_link_type_[node_to];
+  return 0;
+}
+
+int
+KFDNode::get_io_link_weight(uint32_t node_to, uint64_t *weight) {
+  assert(weight != nullptr);
+  if (weight == nullptr) {
+    return EINVAL;
+  }
+  if (io_link_weight_.find(node_to) == io_link_weight_.end()) {
+    return EINVAL;
+  }
+  *weight = io_link_weight_[node_to];
+  return 0;
+}
+
 }  // namespace smi
 }  // namespace amd

projects/amdsmi/src/rocm_smi_main.cc

@@ -280,6 +280,17 @@ RocmSMI::Initialize(uint64_t flags) {
                  "Failed to initialize rocm_smi library (KFD node discovery).");
   }
 
+  std::map<std::pair<uint32_t, uint32_t>, std::shared_ptr<IOLink>>
+    io_link_map_tmp;
+  ret = DiscoverIOLinks(&io_link_map_tmp);
+  if (ret != 0) {
+    throw amd::smi::rsmi_exception(RSMI_INITIALIZATION_ERROR,
+                 "Failed to initialize rocm_smi library (IO Links discovery).");
+  }
+  std::map<std::pair<uint32_t, uint32_t>, std::shared_ptr<IOLink>>::iterator it;
+  for (it = io_link_map_tmp.begin(); it != io_link_map_tmp.end(); it++)
+    io_link_map_[it->first] = it->second;
+
   std::shared_ptr<amd::smi::Device> dev;
 
   // 1. construct kfd_node_map_ with gpu_id as key and *Device as value
@@ -295,6 +306,7 @@ RocmSMI::Initialize(uint64_t flags) {
     }
 
     tmp_map[bdfid]->set_amdgpu_dev_index(dv_ind);
+    dev_ind_to_node_ind_map_[dv_ind] = tmp_map[bdfid]->node_index();
     uint64_t gpu_id = tmp_map[bdfid]->gpu_id();
     dev->set_kfd_gpu_id(gpu_id);
     kfd_node_map_[gpu_id] = tmp_map[bdfid];
@@ -591,5 +603,27 @@ uint32_t RocmSMI::IterateSMIDevices(
   return 0;
 }
 
+int RocmSMI::get_node_index(uint32_t dv_ind, uint32_t *node_ind) {
+  if (dev_ind_to_node_ind_map_.find(dv_ind) == dev_ind_to_node_ind_map_.end()) {
+    return EINVAL;
+  }
+  *node_ind = dev_ind_to_node_ind_map_[dv_ind];
+  return 0;
+}
+
+int RocmSMI::get_io_link_weight(uint32_t node_from, uint32_t node_to,
+                                uint64_t *weight) {
+  assert(weight != nullptr);
+  if (weight == nullptr) {
+    return EINVAL;
+  }
+  if (io_link_map_.find(std::make_pair(node_from, node_to)) ==
+      io_link_map_.end()) {
+    return EINVAL;
+  }
+  *weight = io_link_map_[std::make_pair(node_from, node_to)]->weight();
+  return 0;
+}
+
 }  // namespace smi
 }  // namespace amd