CUDA: Support CUDA Virtual Devices (#25228)

* support cuda virtual devices

* disable NCCL path when virtual devices are used

* label virtual devices in description; add GPUx2 server CI jobs

* code refactor

.github/workflows/server-self-hosted.yml

@@ -143,6 +143,24 @@ jobs:
           export LLAMA_ARG_BACKEND_SAMPLING=1
           pytest -v -x -m "not slow"
 
+      - name: Tests (GPUx2)
+        id: server_integration_tests_gpu2
+        if: ${{ !github.event.pull_request }}
+        run: |
+          cd tools/server/tests
+          source venv/bin/activate
+          export GGML_CUDA_DEVICES=2
+          pytest -v -x -m "not slow"
+
+      - name: Tests (GPUx2, backend-sampling)
+        id: server_integration_tests_gpu2_backend_sampling
+        if: ${{ !github.event.pull_request }}
+        run: |
+          cd tools/server/tests
+          source venv/bin/activate
+          export GGML_CUDA_DEVICES=2 LLAMA_ARG_BACKEND_SAMPLING=1
+          pytest -v -x -m "not slow"
+
   server-kleidiai:
     runs-on: ah-ubuntu_22_04-c8g_8x
 

ggml/src/ggml-cuda/common.cuh

@@ -1115,7 +1115,8 @@ struct ggml_cuda_type_traits<GGML_TYPE_IQ3_S> {
 //////////////////////
 
 struct ggml_cuda_device_info {
-    int device_count;
+    int device_count;           // number of (possibly virtual) devices exposed to the rest of ggml
+    int physical_device_count;  // number of physical CUDA devices actually present
 
     struct cuda_device_info {
         int     cc;                             // compute capability
@@ -1128,6 +1129,9 @@ struct ggml_cuda_device_info {
         size_t  total_vram;
         int     warp_size;                      // Number of threads in a dispatch
         bool    supports_cooperative_launch;    // whether cooperative launch is supported
+        int     physical_device;                // backing physical CUDA device for this (virtual) device
+        int     physical_share_count;           // number of (virtual) devices sharing this device's physical GPU
+        int     virtual_index;                  // index of this (virtual) device among those sharing its physical GPU
     };
 
     cuda_device_info devices[GGML_CUDA_MAX_DEVICES] = {};

ggml/src/ggml-cuda/ggml-cuda.cu

@@ -105,17 +105,27 @@ void ggml_cuda_error(const char * stmt, const char * func, const char * file, in
     GGML_ABORT(GGML_CUDA_NAME " error");
 }
 
+// map a (possibly virtual) device id to the physical CUDA device that backs it
+static int ggml_cuda_get_physical_device(int device) {
+    const ggml_cuda_device_info & info = ggml_cuda_info();
+    GGML_ASSERT(device >= 0 && device < info.device_count);
+    return info.devices[device].physical_device;
+}
+
 // this is faster on Windows
 // probably because the Windows CUDA libraries forget to make this check before invoking the drivers
 void ggml_cuda_set_device(int device) {
+    // translate the (possibly virtual) device id to the physical CUDA device that backs it
+    const int physical_device = ggml_cuda_get_physical_device(device);
+
     int current_device;
     CUDA_CHECK(cudaGetDevice(&current_device));
 
-    if (device == current_device) {
+    if (physical_device == current_device) {
         return;
     }
 
-    CUDA_CHECK(cudaSetDevice(device));
+    CUDA_CHECK(cudaSetDevice(physical_device));
 }
 
 int ggml_cuda_get_device() {
@@ -206,48 +216,90 @@ static int ggml_cuda_parse_id(char devName[]) {
 static ggml_cuda_device_info ggml_cuda_init() {
     ggml_cuda_device_info info = {};
 
-    cudaError_t err = cudaGetDeviceCount(&info.device_count);
+    cudaError_t err = cudaGetDeviceCount(&info.physical_device_count);
     if (err != cudaSuccess) {
         GGML_LOG_ERROR("%s: failed to initialize " GGML_CUDA_NAME ": %s\n", __func__, cudaGetErrorString(err));
         return info;
     }
 
-    GGML_ASSERT(info.device_count <= GGML_CUDA_MAX_DEVICES);
+    GGML_ASSERT(info.physical_device_count <= GGML_CUDA_MAX_DEVICES);
+
+    // by default expose exactly the physical devices; GGML_CUDA_DEVICES can request a different
+    // number of (virtual) devices to emulate multi-GPU systems on a machine with fewer GPUs
+    info.device_count = info.physical_device_count;
+
+    const char * devices_env = getenv("GGML_CUDA_DEVICES");
+    if (devices_env != nullptr && info.physical_device_count > 0) {
+        const int requested = atoi(devices_env);
+        if (requested > 0) {
+            info.device_count = requested;
+        } else {
+            GGML_LOG_WARN("%s: ignoring invalid GGML_CUDA_DEVICES=\"%s\"\n", __func__, devices_env);
+        }
+    }
+
+    if (info.device_count > GGML_CUDA_MAX_DEVICES) {
+        GGML_LOG_WARN("%s: requested %d devices, clamping to GGML_CUDA_MAX_DEVICES=%d\n",
+                      __func__, info.device_count, GGML_CUDA_MAX_DEVICES);
+        info.device_count = GGML_CUDA_MAX_DEVICES;
+    }
+
+    // map each (virtual) device to a backing physical device (round-robin), assign each its index
+    // among the (virtual) devices sharing that physical GPU, and store the per-physical share count
+    int physical_share_count[GGML_CUDA_MAX_DEVICES] = {};
+    GGML_ASSERT(info.device_count == 0 || info.physical_device_count > 0);
+    for (int id = 0; id < info.device_count; ++id) {
+        info.devices[id].physical_device = id % info.physical_device_count;
+        info.devices[id].virtual_index  = physical_share_count[info.devices[id].physical_device]++;
+    }
 
     int64_t total_vram = 0;
-    for (int id = 0; id < info.device_count; ++id) {
+    for (int id = 0; id < info.physical_device_count; ++id) {
         cudaDeviceProp prop;
         CUDA_CHECK(cudaGetDeviceProperties(&prop, id));
         total_vram += prop.totalGlobalMem;
     }
     GGML_LOG_INFO("%s: found %d " GGML_CUDA_NAME " devices (Total VRAM: %zu MiB):\n",
-                  __func__, info.device_count, (size_t)(total_vram / (1024 * 1024)));
+                  __func__, info.physical_device_count, (size_t)(total_vram / (1024 * 1024)));
+    if (info.device_count != info.physical_device_count) {
+        GGML_LOG_INFO("%s: emulating %d virtual device(s) on %d physical device(s) (GGML_CUDA_DEVICES)\n",
+                      __func__, info.device_count, info.physical_device_count);
+    }
     total_vram = 0;
 
     std::vector<std::pair<int, std::string>> turing_devices_without_mma;
     for (int id = 0; id < info.device_count; ++id) {
+        const int physical_id = info.devices[id].physical_device;
+
         int device_vmm = 0;
 
 #if defined(GGML_USE_VMM)
         CUdevice device;
-        CU_CHECK(cuDeviceGet(&device, id));
+        CU_CHECK(cuDeviceGet(&device, physical_id));
         CU_CHECK(cuDeviceGetAttribute(&device_vmm, CU_DEVICE_ATTRIBUTE_VIRTUAL_MEMORY_MANAGEMENT_SUPPORTED, device));
 
         if (device_vmm) {
             CUmemAllocationProp alloc_prop = {};
             alloc_prop.type = CU_MEM_ALLOCATION_TYPE_PINNED;
             alloc_prop.location.type = CU_MEM_LOCATION_TYPE_DEVICE;
-            alloc_prop.location.id = id;
+            alloc_prop.location.id = physical_id;
             CU_CHECK(cuMemGetAllocationGranularity(&info.devices[id].vmm_granularity, &alloc_prop, CU_MEM_ALLOC_GRANULARITY_RECOMMENDED));
         }
 #endif // defined(GGML_USE_VMM)
         info.devices[id].vmm = !!device_vmm;
 
         cudaDeviceProp prop;
-        CUDA_CHECK(cudaGetDeviceProperties(&prop, id));
+        CUDA_CHECK(cudaGetDeviceProperties(&prop, physical_id));
+
+        // a virtual device owns only a share of its physical GPU's memory; report that share so the
+        // logged per-device VRAM sums to the physical total above.
+        GGML_ASSERT(physical_share_count[physical_id] > 0);
+        info.devices[id].physical_share_count = physical_share_count[physical_id];
+        const size_t device_vram = prop.totalGlobalMem / info.devices[id].physical_share_count;
+        const size_t device_vram_mib = device_vram / (1024 * 1024);
 
         info.default_tensor_split[id] = total_vram;
-        total_vram += prop.totalGlobalMem;
+        total_vram += device_vram;
 #if defined(GGML_USE_HIP)
         info.devices[id].integrated = prop.integrated;
 #else
@@ -259,7 +311,7 @@ static ggml_cuda_device_info ggml_cuda_init() {
 
 #ifndef GGML_USE_MUSA
         int supports_coop_launch = 0;
-        CUDA_CHECK(cudaDeviceGetAttribute(&supports_coop_launch, cudaDevAttrCooperativeLaunch, id));
+        CUDA_CHECK(cudaDeviceGetAttribute(&supports_coop_launch, cudaDevAttrCooperativeLaunch, physical_id));
         info.devices[id].supports_cooperative_launch = !!supports_coop_launch;
 #else
         info.devices[id].supports_cooperative_launch = false;
@@ -282,7 +334,7 @@ static ggml_cuda_device_info ggml_cuda_init() {
         GGML_LOG_INFO("  Device %d: %s, %s (0x%x), VMM: %s, Wave Size: %d, VRAM: %zu MiB\n",
                       id, prop.name, prop.gcnArchName, info.devices[id].cc & 0xffff,
                       device_vmm ? "yes" : "no", prop.warpSize,
-                      (size_t)(prop.totalGlobalMem / (1024 * 1024)));
+                      device_vram_mib);
 #elif defined(GGML_USE_MUSA)
         // FIXME: Ensure compatibility with varying warp sizes across different MUSA archs.
         info.devices[id].warp_size = 32;
@@ -291,13 +343,13 @@ static ggml_cuda_device_info ggml_cuda_init() {
         info.devices[id].cc += prop.minor * 0x10;
         GGML_LOG_INFO("  Device %d: %s, compute capability %d.%d, VMM: %s, VRAM: %zu MiB\n",
                       id, prop.name, prop.major, prop.minor, device_vmm ? "yes" : "no",
-                      (size_t)(prop.totalGlobalMem / (1024 * 1024)));
+                      device_vram_mib);
 #else
         info.devices[id].smpbo = prop.sharedMemPerBlockOptin;
         info.devices[id].cc = 100*prop.major + 10*prop.minor;
         GGML_LOG_INFO("  Device %d: %s, compute capability %d.%d, VMM: %s, VRAM: %zu MiB\n",
                       id, prop.name, prop.major, prop.minor, device_vmm ? "yes" : "no",
-                      (size_t)(prop.totalGlobalMem / (1024 * 1024)));
+                      device_vram_mib);
         std::string device_name(prop.name);
         if (device_name == "NVIDIA GeForce MX450") {
             turing_devices_without_mma.push_back({ id, device_name });
@@ -312,7 +364,7 @@ static ggml_cuda_device_info ggml_cuda_init() {
         // TODO: Check for future drivers the default scheduling strategy and
         // remove this call again when cudaDeviceScheduleSpin is default.
         if (prop.major == 12 && prop.minor == 1) {
-            CUDA_CHECK(cudaSetDevice(id));
+            CUDA_CHECK(cudaSetDevice(physical_id));
             CUDA_CHECK(cudaSetDeviceFlags(cudaDeviceScheduleSpin));
         }
 
@@ -337,9 +389,9 @@ static ggml_cuda_device_info ggml_cuda_init() {
     // CUBLAS_CHECK(cublasLoggerConfigure(1, 1, 0, nullptr));
 
     if (getenv("GGML_CUDA_P2P") != nullptr) {
-        for (int id = 0; id < info.device_count; ++id) {
-            ggml_cuda_set_device(id);
-            for (int id_other = 0; id_other < info.device_count; ++id_other) {
+        for (int id = 0; id < info.physical_device_count; ++id) {
+            CUDA_CHECK(cudaSetDevice(id));
+            for (int id_other = 0; id_other < info.physical_device_count; ++id_other) {
                 if (id == id_other) {
                     continue;
                 }
@@ -484,6 +536,7 @@ struct ggml_cuda_pool_vmm : public ggml_cuda_pool {
     static const size_t CUDA_POOL_VMM_MAX_SIZE = 1ull << 35; // 32 GB
 
     int device;
+    int physical_device;
     CUdeviceptr pool_addr = 0;
     size_t pool_used = 0;
     size_t pool_size = 0;
@@ -494,6 +547,7 @@ struct ggml_cuda_pool_vmm : public ggml_cuda_pool {
 
     explicit ggml_cuda_pool_vmm(int device) :
         device(device),
+        physical_device(ggml_cuda_get_physical_device(device)),
         granularity(ggml_cuda_info().devices[device].vmm_granularity) {
     }
 
@@ -529,7 +583,7 @@ struct ggml_cuda_pool_vmm : public ggml_cuda_pool {
             CUmemAllocationProp prop = {};
             prop.type = CU_MEM_ALLOCATION_TYPE_PINNED;
             prop.location.type = CU_MEM_LOCATION_TYPE_DEVICE;
-            prop.location.id = device;
+            prop.location.id = physical_device;
             CUmemGenericAllocationHandle handle;
             CU_CHECK(cuMemCreate(&handle, reserve_size, &prop, 0));
 
@@ -558,20 +612,28 @@ struct ggml_cuda_pool_vmm : public ggml_cuda_pool {
                 // NCCL implicitly enables peer access (cudaDeviceEnablePeerAccess), and
                 // GGML_CUDA_P2P enables it explicitly. Unlike cudaMalloc buffers, VMM
                 // allocations do not become peer-accessible from that alone, so access
-                // must be granted explicitly here.
+                // must be granted explicitly here. With virtual devices, grant access
+                // on the backing *physical* devices (deduplicated, since several
+                // virtual devices can map to the same physical GPU).
                 std::vector<CUmemAccessDesc> access_descs;
+                bool physical_seen[GGML_CUDA_MAX_DEVICES] = {};
                 const int device_count = ggml_cuda_info().device_count;
                 for (int id = 0; id < device_count; ++id) {
-                    if (id != device) {
+                    const int id_physical = ggml_cuda_get_physical_device(id);
+                    if (id_physical != physical_device) {
                         int can_access_peer = 0;
-                        CUDA_CHECK(cudaDeviceCanAccessPeer(&can_access_peer, id, device));
+                        CUDA_CHECK(cudaDeviceCanAccessPeer(&can_access_peer, id_physical, physical_device));
                         if (!can_access_peer) {
                             continue;
                         }
                     }
+                    if (physical_seen[id_physical]) {
+                        continue;
+                    }
+                    physical_seen[id_physical] = true;
                     CUmemAccessDesc access = {};
                     access.location.type = CU_MEM_LOCATION_TYPE_DEVICE;
-                    access.location.id = id;
+                    access.location.id = id_physical;
                     access.flags = CU_MEM_ACCESS_FLAGS_PROT_READWRITE;
                     access_descs.push_back(access);
                 }
@@ -580,7 +642,7 @@ struct ggml_cuda_pool_vmm : public ggml_cuda_pool {
                 // set access for non P2P
                 CUmemAccessDesc access = {};
                 access.location.type = CU_MEM_LOCATION_TYPE_DEVICE;
-                access.location.id = device;
+                access.location.id = physical_device;
                 access.flags = CU_MEM_ACCESS_FLAGS_PROT_READWRITE;
                 CU_CHECK(cuMemSetAccess(start_ptr, reserve_size, &access, 1));
             }
@@ -756,13 +818,17 @@ static bool ggml_backend_cuda_buffer_cpy_tensor(ggml_backend_buffer_t buffer, co
     if (ggml_backend_buffer_is_cuda(src->buffer)) {
         ggml_backend_cuda_buffer_context * src_ctx = (ggml_backend_cuda_buffer_context *)src->buffer->context;
         ggml_backend_cuda_buffer_context * dst_ctx = (ggml_backend_cuda_buffer_context *)dst->buffer->context;
-        if (src_ctx->device == dst_ctx->device) {
+        // compare the backing physical devices: distinct virtual devices may share one physical GPU,
+        // in which case a same-device copy (not a peer copy) is required
+        const int src_physical = ggml_cuda_get_physical_device(src_ctx->device);
+        const int dst_physical = ggml_cuda_get_physical_device(dst_ctx->device);
+        if (src_physical == dst_physical) {
             CUDA_CHECK(cudaMemcpyAsync(dst->data, src->data, ggml_nbytes(src), cudaMemcpyDeviceToDevice, cudaStreamPerThread));
         } else {
 #ifdef GGML_CUDA_NO_PEER_COPY
             return false;
 #else
-            CUDA_CHECK(cudaMemcpyPeerAsync(dst->data, dst_ctx->device, src->data, src_ctx->device, ggml_nbytes(src), cudaStreamPerThread));
+            CUDA_CHECK(cudaMemcpyPeerAsync(dst->data, dst_physical, src->data, src_physical, ggml_nbytes(src), cudaStreamPerThread));
 #endif
         }
         CUDA_CHECK(cudaStreamSynchronize(cudaStreamPerThread));
@@ -1104,6 +1170,15 @@ static void ggml_backend_cuda_comm_init_internal(ggml_backend_cuda_comm_context
 
 static void ggml_backend_cuda_comm_init_nccl(ggml_backend_cuda_comm_context * ret) {
 #ifdef GGML_USE_NCCL
+    // Disabling NCCL path when CUDA virtual devices are in use since NCCL requires one distinct physical GPU per rank.
+    const ggml_cuda_device_info & info = ggml_cuda_info();
+    if (info.device_count > info.physical_device_count) {
+        GGML_LOG_WARN("NCCL disabled: virtual devices in use; "
+                      "falling back to internal AllReduce\n");
+        ggml_backend_cuda_comm_init_internal(ret);
+        return;
+    }
+
     const size_t n = ret->dev_ids.size();
     ret->comms.resize(n);
     ncclResult_t rc = ncclCommInitAll(ret->comms.data(), (int) n, ret->dev_ids.data());
@@ -2363,13 +2438,17 @@ static bool ggml_backend_cuda_cpy_tensor_async(ggml_backend_t backend_src, ggml_
 
     if (backend_src != backend_dst) {
         // copy on src stream
-        if (cuda_ctx_src->device == cuda_ctx_dst->device) {
+        // compare the backing physical devices: distinct virtual devices may share one physical GPU,
+        // in which case a same-device copy (not a peer copy) is required
+        const int src_physical = ggml_cuda_get_physical_device(cuda_ctx_src->device);
+        const int dst_physical = ggml_cuda_get_physical_device(cuda_ctx_dst->device);
+        if (src_physical == dst_physical) {
             CUDA_CHECK(cudaMemcpyAsync(dst->data, src->data, ggml_nbytes(dst), cudaMemcpyDeviceToDevice, cuda_ctx_src->stream()));
         } else {
 #ifdef GGML_CUDA_NO_PEER_COPY
             return false;
 #else
-            CUDA_CHECK(cudaMemcpyPeerAsync(dst->data, cuda_ctx_dst->device, src->data, cuda_ctx_src->device, ggml_nbytes(dst), cuda_ctx_src->stream()));
+            CUDA_CHECK(cudaMemcpyPeerAsync(dst->data, dst_physical, src->data, src_physical, ggml_nbytes(dst), cuda_ctx_src->stream()));
 #endif // GGML_CUDA_NO_PEER_COPY
         }
 
@@ -4354,16 +4433,38 @@ int ggml_backend_cuda_get_device_count() {
     return ggml_cuda_info().device_count;
 }
 
-void ggml_backend_cuda_get_device_description(int device, char * description, size_t description_size) {
+static std::string ggml_cuda_device_description(int device) {
     cudaDeviceProp prop;
-    CUDA_CHECK(cudaGetDeviceProperties(&prop, device));
-    snprintf(description, description_size, "%s", prop.name);
+    CUDA_CHECK(cudaGetDeviceProperties(&prop, ggml_cuda_get_physical_device(device)));
+
+    const ggml_cuda_device_info & info = ggml_cuda_info();
+    std::string description = prop.name;
+    if (info.device_count > info.physical_device_count) {
+        description += " (physical device " + std::to_string(info.devices[device].physical_device) +
+                       ", virtual device " + std::to_string(info.devices[device].virtual_index) + ")";
+    }
+    return description;
+}
+
+void ggml_backend_cuda_get_device_description(int device, char * description, size_t description_size) {
+    snprintf(description, description_size, "%s", ggml_cuda_device_description(device).c_str());
+}
+
+static int ggml_cuda_physical_device_share_count(int device) {
+    const ggml_cuda_device_info & info = ggml_cuda_info();
+    GGML_ASSERT(device >= 0 && device < info.device_count);
+    return info.devices[device].physical_share_count;
 }
 
 void ggml_backend_cuda_get_device_memory(int device, size_t * free, size_t * total) {
     ggml_cuda_set_device(device);
 
     CUDA_CHECK(cudaMemGetInfo(free, total));
+
+    // virtual devices sharing one physical GPU share its memory pool; split it between them
+    const int share_count = ggml_cuda_physical_device_share_count(device);
+    *free  /= share_count;
+    *total /= share_count;
 }
 
 bool ggml_backend_cuda_register_host_buffer(void * buffer, size_t size) {
@@ -4514,7 +4615,7 @@ static void ggml_backend_cuda_device_get_memory(ggml_backend_dev_t dev, size_t *
 #if defined(__linux__)
     // Check if this is a UMA (Unified Memory Architecture) system
     cudaDeviceProp prop;
-    CUDA_CHECK(cudaGetDeviceProperties(&prop, ctx->device));
+    CUDA_CHECK(cudaGetDeviceProperties(&prop, ggml_cuda_get_physical_device(ctx->device)));
 
     // Check if UMA is explicitly enabled via environment variable
     bool uma_env = getenv("GGML_CUDA_ENABLE_UNIFIED_MEMORY") != nullptr;
@@ -4533,13 +4634,17 @@ static void ggml_backend_cuda_device_get_memory(ggml_backend_dev_t dev, size_t *
     }
 #endif // defined(__linux__)
 
+    // virtual devices sharing one physical GPU share its memory pool; split it between them
+    const int share_count = ggml_cuda_physical_device_share_count(ctx->device);
+    *free  /= share_count;
+    *total /= share_count;
 }
 
 static enum ggml_backend_dev_type ggml_backend_cuda_device_get_type(ggml_backend_dev_t dev) {
     ggml_backend_cuda_device_context * ctx = (ggml_backend_cuda_device_context *) dev->context;
 
     cudaDeviceProp prop;
-    CUDA_CHECK(cudaGetDeviceProperties(&prop, ctx->device));
+    CUDA_CHECK(cudaGetDeviceProperties(&prop, ggml_cuda_get_physical_device(ctx->device)));
 
     return prop.integrated
         ? GGML_BACKEND_DEVICE_TYPE_IGPU
@@ -5199,18 +5304,24 @@ ggml_backend_reg_t ggml_backend_cuda_reg() {
             ggml_backend_cuda_reg_context * ctx = new ggml_backend_cuda_reg_context;
             const int min_batch_size = getenv("GGML_OP_OFFLOAD_MIN_BATCH") ? atoi(getenv("GGML_OP_OFFLOAD_MIN_BATCH")) : 32;
 
-            for (int i = 0; i < ggml_cuda_info().device_count; i++) {
+            const ggml_cuda_device_info & info = ggml_cuda_info();
+            const bool virtual_devices = info.device_count > info.physical_device_count;
+
+            for (int i = 0; i < info.device_count; i++) {
+                const int physical_id = info.devices[i].physical_device;
+
                 ggml_backend_cuda_device_context * dev_ctx = new ggml_backend_cuda_device_context;
                 dev_ctx->device = i;
                 dev_ctx->name = GGML_CUDA_NAME + std::to_string(i);
-
-                cudaDeviceProp prop;
-                CUDA_CHECK(cudaGetDeviceProperties(&prop, i));
-                dev_ctx->description = prop.name;
+                dev_ctx->description = ggml_cuda_device_description(i);
 
                 char pci_bus_id[32] = {};
-                CUDA_CHECK(cudaDeviceGetPCIBusId(pci_bus_id, sizeof(pci_bus_id), i));
+                CUDA_CHECK(cudaDeviceGetPCIBusId(pci_bus_id, sizeof(pci_bus_id), physical_id));
                 dev_ctx->pci_bus_id = pci_bus_id;
+                if (virtual_devices) {
+                    // make the pci bus id unique for virtual devices
+                    dev_ctx->pci_bus_id += "-v" + std::to_string(i);
+                }
                 for (char & c : dev_ctx->pci_bus_id) {
                     c = std::tolower(c);
                 }