{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "618fd23a",
   "metadata": {
    "origin_pos": 0
   },
   "source": [
    "# GPU\n",
    ":label:`sec_use_gpu`\n",
    "\n",
    "在 :numref:`tab_intro_decade`中，\n",
    "我们回顾了过去20年计算能力的快速增长。\n",
    "简而言之，自2000年以来，GPU性能每十年增长1000倍。\n",
    "\n",
    "本节，我们将讨论如何利用这种计算性能进行研究。\n",
    "首先是如何使用单个GPU，然后是如何使用多个GPU和多个服务器（具有多个GPU）。\n",
    "\n",
    "我们先看看如何使用单个NVIDIA GPU进行计算。\n",
    "首先，确保至少安装了一个NVIDIA GPU。\n",
    "然后，下载[NVIDIA驱动和CUDA](https://developer.nvidia.com/cuda-downloads)\n",
    "并按照提示设置适当的路径。\n",
    "当这些准备工作完成，就可以使用`nvidia-smi`命令来(**查看显卡信息。**)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "369d9baa",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:06.499888Z",
     "iopub.status.busy": "2023-08-18T06:58:06.499324Z",
     "iopub.status.idle": "2023-08-18T06:58:06.859541Z",
     "shell.execute_reply": "2023-08-18T06:58:06.858210Z"
    },
    "origin_pos": 1,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Fri Aug 18 06:58:06 2023       \r\n",
      "+-----------------------------------------------------------------------------+\r\n",
      "| NVIDIA-SMI 470.161.03   Driver Version: 470.161.03   CUDA Version: 11.7     |\r\n",
      "|-------------------------------+----------------------+----------------------+\r\n",
      "| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |\r\n",
      "| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |\r\n",
      "|                               |                      |               MIG M. |\r\n",
      "|===============================+======================+======================|\r\n",
      "|   0  Tesla V100-SXM2...  Off  | 00000000:00:1B.0 Off |                    0 |\r\n",
      "| N/A   41C    P0    42W / 300W |      0MiB / 16160MiB |      0%      Default |\r\n",
      "|                               |                      |                  N/A |\r\n",
      "+-------------------------------+----------------------+----------------------+\r\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|   1  Tesla V100-SXM2...  Off  | 00000000:00:1C.0 Off |                    0 |\r\n",
      "| N/A   44C    P0   113W / 300W |   1456MiB / 16160MiB |     53%      Default |\r\n",
      "|                               |                      |                  N/A |\r\n",
      "+-------------------------------+----------------------+----------------------+\r\n",
      "|   2  Tesla V100-SXM2...  Off  | 00000000:00:1D.0 Off |                    0 |\r\n",
      "| N/A   43C    P0   120W / 300W |   1358MiB / 16160MiB |     55%      Default |\r\n",
      "|                               |                      |                  N/A |\r\n",
      "+-------------------------------+----------------------+----------------------+\r\n",
      "|   3  Tesla V100-SXM2...  Off  | 00000000:00:1E.0 Off |                    0 |\r\n",
      "| N/A   42C    P0    47W / 300W |      0MiB / 16160MiB |      0%      Default |\r\n",
      "|                               |                      |                  N/A |\r\n",
      "+-------------------------------+----------------------+----------------------+\r\n",
      "                                                                               \r\n",
      "+-----------------------------------------------------------------------------+\r\n",
      "| Processes:                                                                  |\r\n",
      "|  GPU   GI   CI        PID   Type   Process name                  GPU Memory |\r\n",
      "|        ID   ID                                                   Usage      |\r\n",
      "|=============================================================================|\r\n",
      "+-----------------------------------------------------------------------------+\r\n"
     ]
    }
   ],
   "source": [
    "!nvidia-smi"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "23e1982b",
   "metadata": {
    "origin_pos": 3,
    "tab": [
     "pytorch"
    ]
   },
   "source": [
    "在PyTorch中，每个数组都有一个设备（device），\n",
    "我们通常将其称为环境（context）。\n",
    "默认情况下，所有变量和相关的计算都分配给CPU。\n",
    "有时环境可能是GPU。\n",
    "当我们跨多个服务器部署作业时，事情会变得更加棘手。\n",
    "通过智能地将数组分配给环境，\n",
    "我们可以最大限度地减少在设备之间传输数据的时间。\n",
    "例如，当在带有GPU的服务器上训练神经网络时，\n",
    "我们通常希望模型的参数在GPU上。\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "aeacf63c",
   "metadata": {
    "origin_pos": 5
   },
   "source": [
    "要运行此部分中的程序，至少需要两个GPU。\n",
    "注意，对大多数桌面计算机来说，这可能是奢侈的，但在云中很容易获得。\n",
    "例如可以使用AWS EC2的多GPU实例。\n",
    "本书的其他章节大都不需要多个GPU，\n",
    "而本节只是为了展示数据如何在不同的设备之间传递。\n",
    "\n",
    "## [**计算设备**]\n",
    "\n",
    "我们可以指定用于存储和计算的设备，如CPU和GPU。\n",
    "默认情况下，张量是在内存中创建的，然后使用CPU计算它。\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "872e46f0",
   "metadata": {
    "origin_pos": 7,
    "tab": [
     "pytorch"
    ]
   },
   "source": [
    "在PyTorch中，CPU和GPU可以用`torch.device('cpu')`\n",
    "和`torch.device('cuda')`表示。\n",
    "应该注意的是，`cpu`设备意味着所有物理CPU和内存，\n",
    "这意味着PyTorch的计算将尝试使用所有CPU核心。\n",
    "然而，`gpu`设备只代表一个卡和相应的显存。\n",
    "如果有多个GPU，我们使用`torch.device(f'cuda:{i}')`\n",
    "来表示第$i$块GPU（$i$从0开始）。\n",
    "另外，`cuda:0`和`cuda`是等价的。\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "9f69ad46",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:06.865430Z",
     "iopub.status.busy": "2023-08-18T06:58:06.864979Z",
     "iopub.status.idle": "2023-08-18T06:58:07.970615Z",
     "shell.execute_reply": "2023-08-18T06:58:07.969801Z"
    },
    "origin_pos": 10,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(device(type='cpu'), device(type='cuda'), device(type='cuda', index=1))"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import torch\n",
    "from torch import nn\n",
    "\n",
    "torch.device('cpu'), torch.device('cuda'), torch.device('cuda:1')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "248784cc",
   "metadata": {
    "origin_pos": 13
   },
   "source": [
    "我们可以(**查询可用gpu的数量。**)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "c29151b0",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:07.974568Z",
     "iopub.status.busy": "2023-08-18T06:58:07.973917Z",
     "iopub.status.idle": "2023-08-18T06:58:07.979097Z",
     "shell.execute_reply": "2023-08-18T06:58:07.978337Z"
    },
    "origin_pos": 15,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "torch.cuda.device_count()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6e1bc4a6",
   "metadata": {
    "origin_pos": 18
   },
   "source": [
    "现在我们定义了两个方便的函数，\n",
    "[**这两个函数允许我们在不存在所需所有GPU的情况下运行代码。**]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "cda0ab76",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:07.983261Z",
     "iopub.status.busy": "2023-08-18T06:58:07.982604Z",
     "iopub.status.idle": "2023-08-18T06:58:07.990309Z",
     "shell.execute_reply": "2023-08-18T06:58:07.989541Z"
    },
    "origin_pos": 20,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(device(type='cuda', index=0),\n",
       " device(type='cpu'),\n",
       " [device(type='cuda', index=0), device(type='cuda', index=1)])"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def try_gpu(i=0):  #@save\n",
    "    \"\"\"如果存在，则返回gpu(i)，否则返回cpu()\"\"\"\n",
    "    if torch.cuda.device_count() >= i + 1:\n",
    "        return torch.device(f'cuda:{i}')\n",
    "    return torch.device('cpu')\n",
    "\n",
    "def try_all_gpus():  #@save\n",
    "    \"\"\"返回所有可用的GPU，如果没有GPU，则返回[cpu(),]\"\"\"\n",
    "    devices = [torch.device(f'cuda:{i}')\n",
    "             for i in range(torch.cuda.device_count())]\n",
    "    return devices if devices else [torch.device('cpu')]\n",
    "\n",
    "try_gpu(), try_gpu(10), try_all_gpus()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "034b0d3b",
   "metadata": {
    "origin_pos": 23
   },
   "source": [
    "## 张量与GPU\n",
    "\n",
    "我们可以[**查询张量所在的设备。**]\n",
    "默认情况下，张量是在CPU上创建的。\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "f6ab0f26",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:07.994741Z",
     "iopub.status.busy": "2023-08-18T06:58:07.994126Z",
     "iopub.status.idle": "2023-08-18T06:58:07.999439Z",
     "shell.execute_reply": "2023-08-18T06:58:07.998673Z"
    },
    "origin_pos": 25,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "device(type='cpu')"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x = torch.tensor([1, 2, 3])\n",
    "x.device"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f39b0efa",
   "metadata": {
    "origin_pos": 28
   },
   "source": [
    "需要注意的是，无论何时我们要对多个项进行操作，\n",
    "它们都必须在同一个设备上。\n",
    "例如，如果我们对两个张量求和，\n",
    "我们需要确保两个张量都位于同一个设备上，\n",
    "否则框架将不知道在哪里存储结果，甚至不知道在哪里执行计算。\n",
    "\n",
    "### [**存储在GPU上**]\n",
    "\n",
    "有几种方法可以在GPU上存储张量。\n",
    "例如，我们可以在创建张量时指定存储设备。接\n",
    "下来，我们在第一个`gpu`上创建张量变量`X`。\n",
    "在GPU上创建的张量只消耗这个GPU的显存。\n",
    "我们可以使用`nvidia-smi`命令查看显存使用情况。\n",
    "一般来说，我们需要确保不创建超过GPU显存限制的数据。\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "a67dbf2f",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:08.004162Z",
     "iopub.status.busy": "2023-08-18T06:58:08.003541Z",
     "iopub.status.idle": "2023-08-18T06:58:09.277879Z",
     "shell.execute_reply": "2023-08-18T06:58:09.277008Z"
    },
    "origin_pos": 30,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "tensor([[1., 1., 1.],\n",
       "        [1., 1., 1.]], device='cuda:0')"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "X = torch.ones(2, 3, device=try_gpu())\n",
    "X"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "dd17f6d7",
   "metadata": {
    "origin_pos": 33
   },
   "source": [
    "假设我们至少有两个GPU，下面的代码将在(**第二个GPU上创建一个随机张量。**)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "7c0d4a84",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:09.282814Z",
     "iopub.status.busy": "2023-08-18T06:58:09.282230Z",
     "iopub.status.idle": "2023-08-18T06:58:10.279046Z",
     "shell.execute_reply": "2023-08-18T06:58:10.278227Z"
    },
    "origin_pos": 35,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "tensor([[0.4860, 0.1285, 0.0440],\n",
       "        [0.9743, 0.4159, 0.9979]], device='cuda:1')"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Y = torch.rand(2, 3, device=try_gpu(1))\n",
    "Y"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "71646fa2",
   "metadata": {
    "origin_pos": 38
   },
   "source": [
    "### 复制\n",
    "\n",
    "如果我们[**要计算`X + Y`，我们需要决定在哪里执行这个操作**]。\n",
    "例如，如 :numref:`fig_copyto`所示，\n",
    "我们可以将`X`传输到第二个GPU并在那里执行操作。\n",
    "*不要*简单地`X`加上`Y`，因为这会导致异常，\n",
    "运行时引擎不知道该怎么做：它在同一设备上找不到数据会导致失败。\n",
    "由于`Y`位于第二个GPU上，所以我们需要将`X`移到那里，\n",
    "然后才能执行相加运算。\n",
    "\n",
    "![复制数据以在同一设备上执行操作](../img/copyto.svg)\n",
    ":label:`fig_copyto`\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "9e700cd2",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:10.284097Z",
     "iopub.status.busy": "2023-08-18T06:58:10.283529Z",
     "iopub.status.idle": "2023-08-18T06:58:10.290795Z",
     "shell.execute_reply": "2023-08-18T06:58:10.290007Z"
    },
    "origin_pos": 40,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "tensor([[1., 1., 1.],\n",
      "        [1., 1., 1.]], device='cuda:0')\n",
      "tensor([[1., 1., 1.],\n",
      "        [1., 1., 1.]], device='cuda:1')\n"
     ]
    }
   ],
   "source": [
    "Z = X.cuda(1)\n",
    "print(X)\n",
    "print(Z)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f57eab12",
   "metadata": {
    "origin_pos": 42
   },
   "source": [
    "[**现在数据在同一个GPU上（`Z`和`Y`都在），我们可以将它们相加。**]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "b2f04f35",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:10.295377Z",
     "iopub.status.busy": "2023-08-18T06:58:10.294845Z",
     "iopub.status.idle": "2023-08-18T06:58:10.301122Z",
     "shell.execute_reply": "2023-08-18T06:58:10.300297Z"
    },
    "origin_pos": 43,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "tensor([[1.4860, 1.1285, 1.0440],\n",
       "        [1.9743, 1.4159, 1.9979]], device='cuda:1')"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Y + Z"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9acbe573",
   "metadata": {
    "origin_pos": 45,
    "tab": [
     "pytorch"
    ]
   },
   "source": [
    "假设变量`Z`已经存在于第二个GPU上。\n",
    "如果我们还是调用`Z.cuda(1)`会发生什么？\n",
    "它将返回`Z`，而不会复制并分配新内存。\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "d6b95aa1",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:10.305143Z",
     "iopub.status.busy": "2023-08-18T06:58:10.304592Z",
     "iopub.status.idle": "2023-08-18T06:58:10.309707Z",
     "shell.execute_reply": "2023-08-18T06:58:10.308894Z"
    },
    "origin_pos": 48,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Z.cuda(1) is Z"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "35568455",
   "metadata": {
    "origin_pos": 50
   },
   "source": [
    "### 旁注\n",
    "\n",
    "人们使用GPU来进行机器学习，因为单个GPU相对运行速度快。\n",
    "但是在设备（CPU、GPU和其他机器）之间传输数据比计算慢得多。\n",
    "这也使得并行化变得更加困难，因为我们必须等待数据被发送（或者接收），\n",
    "然后才能继续进行更多的操作。\n",
    "这就是为什么拷贝操作要格外小心。\n",
    "根据经验，多个小操作比一个大操作糟糕得多。\n",
    "此外，一次执行几个操作比代码中散布的许多单个操作要好得多。\n",
    "如果一个设备必须等待另一个设备才能执行其他操作，\n",
    "那么这样的操作可能会阻塞。\n",
    "这有点像排队订购咖啡，而不像通过电话预先订购：\n",
    "当客人到店的时候，咖啡已经准备好了。\n",
    "\n",
    "最后，当我们打印张量或将张量转换为NumPy格式时，\n",
    "如果数据不在内存中，框架会首先将其复制到内存中，\n",
    "这会导致额外的传输开销。\n",
    "更糟糕的是，它现在受制于全局解释器锁，使得一切都得等待Python完成。\n",
    "\n",
    "## [**神经网络与GPU**]\n",
    "\n",
    "类似地，神经网络模型可以指定设备。\n",
    "下面的代码将模型参数放在GPU上。\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "587af904",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:10.313163Z",
     "iopub.status.busy": "2023-08-18T06:58:10.312623Z",
     "iopub.status.idle": "2023-08-18T06:58:10.336351Z",
     "shell.execute_reply": "2023-08-18T06:58:10.335568Z"
    },
    "origin_pos": 52,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [],
   "source": [
    "net = nn.Sequential(nn.Linear(3, 1))\n",
    "net = net.to(device=try_gpu())"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a834a04c",
   "metadata": {
    "origin_pos": 55
   },
   "source": [
    "在接下来的几章中，\n",
    "我们将看到更多关于如何在GPU上运行模型的例子，\n",
    "因为它们将变得更加计算密集。\n",
    "\n",
    "当输入为GPU上的张量时，模型将在同一GPU上计算结果。\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "955f7f67",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:10.340989Z",
     "iopub.status.busy": "2023-08-18T06:58:10.340312Z",
     "iopub.status.idle": "2023-08-18T06:58:10.930969Z",
     "shell.execute_reply": "2023-08-18T06:58:10.930143Z"
    },
    "origin_pos": 56,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "tensor([[-0.4275],\n",
       "        [-0.4275]], device='cuda:0', grad_fn=<AddmmBackward0>)"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "net(X)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "fb9f9aef",
   "metadata": {
    "origin_pos": 57
   },
   "source": [
    "让我们(**确认模型参数存储在同一个GPU上。**)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "bd727993",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2023-08-18T06:58:10.935087Z",
     "iopub.status.busy": "2023-08-18T06:58:10.934497Z",
     "iopub.status.idle": "2023-08-18T06:58:10.939740Z",
     "shell.execute_reply": "2023-08-18T06:58:10.938974Z"
    },
    "origin_pos": 59,
    "tab": [
     "pytorch"
    ]
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "device(type='cuda', index=0)"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "net[0].weight.data.device"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "cf1bf3b2",
   "metadata": {
    "origin_pos": 62
   },
   "source": [
    "总之，只要所有的数据和参数都在同一个设备上，\n",
    "我们就可以有效地学习模型。\n",
    "在下面的章节中，我们将看到几个这样的例子。\n",
    "\n",
    "## 小结\n",
    "\n",
    "* 我们可以指定用于存储和计算的设备，例如CPU或GPU。默认情况下，数据在主内存中创建，然后使用CPU进行计算。\n",
    "* 深度学习框架要求计算的所有输入数据都在同一设备上，无论是CPU还是GPU。\n",
    "* 不经意地移动数据可能会显著降低性能。一个典型的错误如下：计算GPU上每个小批量的损失，并在命令行中将其报告给用户（或将其记录在NumPy `ndarray`中）时，将触发全局解释器锁，从而使所有GPU阻塞。最好是为GPU内部的日志分配内存，并且只移动较大的日志。\n",
    "\n",
    "## 练习\n",
    "\n",
    "1. 尝试一个计算量更大的任务，比如大矩阵的乘法，看看CPU和GPU之间的速度差异。再试一个计算量很小的任务呢？\n",
    "1. 我们应该如何在GPU上读写模型参数？\n",
    "1. 测量计算1000个$100 \\times 100$矩阵的矩阵乘法所需的时间，并记录输出矩阵的Frobenius范数，一次记录一个结果，而不是在GPU上保存日志并仅传输最终结果。\n",
    "1. 测量同时在两个GPU上执行两个矩阵乘法与在一个GPU上按顺序执行两个矩阵乘法所需的时间。提示：应该看到近乎线性的缩放。\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "0460f3be",
   "metadata": {
    "origin_pos": 64,
    "tab": [
     "pytorch"
    ]
   },
   "source": [
    "[Discussions](https://discuss.d2l.ai/t/1841)\n"
   ]
  }
 ],
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