{"id":444,"date":"2019-02-21T00:08:29","date_gmt":"2019-02-20T16:08:29","guid":{"rendered":"https:\/\/fick707.com\/?p=444"},"modified":"2019-02-21T00:08:29","modified_gmt":"2019-02-20T16:08:29","slug":"zero-copy","status":"publish","type":"post","link":"https:\/\/fick707.com\/?p=444","title":{"rendered":"zero-copy"},"content":{"rendered":"\n

\u88c5\u8f7d\u81ea\uff1ahttps:\/\/mp.weixin.qq.com\/s?__biz=MzU0MzQ5MDA0Mw==&mid=2247483913&idx=1&sn=2da53737b8e8908cf3efdae9621c9698&chksm=fb0be89dcc7c618b0d5a1ba8ac654295454cfc2fa81fbae5a6de49bf0a91a305ca707e9864fc&scene=21#wechat_redirect
<\/p>\n\n\n

\n

\u6982\u8ff0<\/h2>\n

\u8003\u8651\u8fd9\u6837\u4e00\u79cd\u5e38\u7528\u7684\u60c5\u5f62\uff1a\u4f60\u9700\u8981\u5c06\u9759\u6001\u5185\u5bb9\uff08\u7c7b\u4f3c\u56fe\u7247\u3001\u6587\u4ef6\uff09\u5c55\u793a\u7ed9\u7528\u6237\u3002\u90a3\u4e48\u8fd9\u4e2a\u60c5\u5f62\u5c31\u610f\u5473\u7740\u4f60\u9700\u8981\u5148\u5c06\u9759\u6001\u5185\u5bb9\u4ece\u78c1\u76d8\u4e2d\u62f7\u8d1d\u51fa\u6765\u653e\u5230\u4e00\u4e2a\u5185\u5b58buf\u4e2d\uff0c\u7136\u540e\u5c06\u8fd9\u4e2abuf\u901a\u8fc7socket\u4f20\u8f93\u7ed9\u7528\u6237\uff0c\u8fdb\u800c\u7528\u6237\u6216\u8005\u9759\u6001\u5185\u5bb9\u7684\u5c55\u793a\u3002\u8fd9\u770b\u8d77\u6765\u518d\u6b63\u5e38\u4e0d\u8fc7\u4e86\uff0c\u4f46\u662f\u5b9e\u9645\u4e0a\u8fd9\u662f\u5f88\u4f4e\u6548\u7684\u6d41\u7a0b\uff0c\u6211\u4eec\u628a\u4e0a\u9762\u7684\u8fd9\u79cd\u60c5\u5f62\u62bd\u8c61\u6210\u4e0b\u9762\u7684\u8fc7\u7a0b\uff1a<\/p>\n

read<\/span>(file, tmp_buf, len<\/span>);
write<\/span>(socket, tmp_buf, len<\/span>);
<\/code><\/pre>\n
\u9996\u5148\u8c03\u7528read\u5c06\u9759\u6001\u5185\u5bb9\uff0c\u8fd9\u91cc\u5047\u8bbe\u4e3a\u6587\u4ef6A\uff0c\u8bfb\u53d6\u5230tmp_buf, \u7136\u540e\u8c03\u7528write\u5c06tmp_buf\u5199\u5165\u5230socket\u4e2d\uff0c\u5982\u56fe\uff1a<\/p>\n
<\/figure>\n
\u5728\u8fd9\u4e2a\u8fc7\u7a0b\u4e2d\u6587\u4ef6A\u7684\u7ecf\u5386\u4e864\u6b21copy\u7684\u8fc7\u7a0b\uff1a<\/section>\n

\n
    \n
  1. \n
    \u9996\u5148\uff0c\u8c03\u7528read\u65f6\uff0c\u6587\u4ef6A\u62f7\u8d1d\u5230\u4e86kernel\u6a21\u5f0f\uff1b<\/p>\n<\/li>\n
  2. \n
    \u4e4b\u540e\uff0cCPU\u63a7\u5236\u5c06kernel\u6a21\u5f0f\u6570\u636ecopy\u5230user\u6a21\u5f0f\u4e0b\uff1b<\/p>\n<\/li>\n
  3. \n
    \u8c03\u7528write\u65f6\uff0c\u5148\u5c06user\u6a21\u5f0f\u4e0b\u7684\u5185\u5bb9copy\u5230kernel\u6a21\u5f0f\u4e0b\u7684socket\u7684buffer\u4e2d\uff1b<\/p>\n<\/li>\n
  4. \n
    \u6700\u540e\u5c06kernel\u6a21\u5f0f\u4e0b\u7684socket buffer\u7684\u6570\u636ecopy\u5230\u7f51\u5361\u8bbe\u5907\u4e2d\u4f20\u9001\uff1b<\/p>\n<\/li>\n<\/ol>\n
    \u4ece\u4e0a\u9762\u7684\u8fc7\u7a0b\u53ef\u4ee5\u770b\u51fa\uff0c\u6570\u636e\u767d\u767d\u4ecekernel\u6a21\u5f0f\u5230user\u6a21\u5f0f\u8d70\u4e86\u4e00\u5708\uff0c\u6d6a\u8d39\u4e862\u6b21copy(\u7b2c\u4e00\u6b21\uff0c\u4ecekernel\u6a21\u5f0f\u62f7\u8d1d\u5230user\u6a21\u5f0f\uff1b\u7b2c\u4e8c\u6b21\u4eceuser\u6a21\u5f0f\u518d\u62f7\u8d1d\u56dekernel\u6a21\u5f0f\uff0c\u5373\u4e0a\u97624\u6b21\u8fc7\u7a0b\u7684\u7b2c2\u548c3\u6b65\u9aa4\u3002)\u3002\u800c\u4e14\u4e0a\u9762\u7684\u8fc7\u7a0b\u4e2dkernel\u548cuser\u6a21\u5f0f\u7684\u4e0a\u4e0b\u6587\u7684\u5207\u6362\u4e5f\u662f4\u6b21\u3002<\/p>\n
    \u5e78\u8fd0\u7684\u662f\uff0c\u4f60\u53ef\u4ee5\u7528\u4e00\u79cd\u53eb\u505aZero-Copy\u7684\u6280\u672f\u6765\u53bb\u6389\u8fd9\u4e9b\u65e0\u8c13\u7684copy\u3002\u5e94\u7528\u7a0b\u5e8f\u7528Zero-Copy\u6765\u8bf7\u6c42kernel\u76f4\u63a5\u628adisk\u7684data\u4f20\u8f93\u7ed9socket\uff0c\u800c\u4e0d\u662f\u901a\u8fc7\u5e94\u7528\u7a0b\u5e8f\u4f20\u8f93\u3002Zero-Copy\u5927\u5927\u63d0\u9ad8\u4e86\u5e94\u7528\u7a0b\u5e8f\u7684\u6027\u80fd\uff0c\u5e76\u4e14\u51cf\u5c11\u4e86kernel\u548cuser\u6a21\u5f0f\u4e0a\u4e0b\u6587\u7684\u5207\u6362\u3002<\/p>\n
    \n
    \u8be6\u8ff0<\/h2>\n
    Zero-Copy\u6280\u672f\u7701\u53bb\u4e86\u5c06\u64cd\u4f5c\u7cfb\u7edf\u7684read buffer\u62f7\u8d1d\u5230\u7a0b\u5e8f\u7684buffer\uff0c\u4ee5\u53ca\u4ece\u7a0b\u5e8fbuffer\u62f7\u8d1d\u5230socket buffer\u7684\u6b65\u9aa4\uff0c\u76f4\u63a5\u5c06read buffer\u62f7\u8d1d\u5230socket buffer. Java NIO\u4e2d\u7684FileChannal.transferTo()\u65b9\u6cd5\u5c31\u662f\u8fd9\u6837\u7684\u5b9e\u73b0\uff0c\u8fd9\u4e2a\u5b9e\u73b0\u662f\u4f9d\u8d56\u4e8e\u64cd\u4f5c\u7cfb\u7edf\u5e95\u5c42\u7684sendFile()\u5b9e\u73b0\u7684\u3002<\/p>\n
    public void transferTo(long position, long count, WritableByteChannel target)<\/span>;
    <\/code><\/pre>\n
    \u4ed6\u5e95\u5c42\u7684\u8c03\u7528\u65f6\u7cfb\u7edf\u8c03\u7528sendFile()<\/strong>\u65b9\u6cd5\uff1a<\/p>\n
    #include <sys\/socket.h><\/span>
    ssize_t<\/span> sendfile(int<\/span> out_fd, int<\/span> in_fd, off_t<\/span> *offset, size_t<\/span> count);
    <\/code><\/pre>\n
    \u4e0b\u56fe\u5c55\u793a\u4e86\u5728transferTo()\u4e4b\u540e\u7684\u6570\u636e\u6d41\u5411\uff1a<\/p>\n
    <\/p>\n
    <\/figure>\n
    \u4e0b\u56fe\u5c55\u793a\u4e86\u5728\u4f7f\u7528transferTo()\u4e4b\u540e\u7684\u4e0a\u4e0b\u6587\u5207\u6362\uff1a<\/p>\n
    <\/p>\n
    \u4f7f\u7528\u4e86Zero-Copy\u6280\u672f\u4e4b\u540e\uff0c\u6574\u4e2a\u8fc7\u7a0b\u5982\u4e0b\uff1a<\/p>\n
      \n
    1. \n
      transferTo()\u65b9\u6cd5\u4f7f\u5f97\u6587\u4ef6A\u7684\u5185\u5bb9\u76f4\u63a5\u62f7\u8d1d\u5230\u4e00\u4e2aread buffer\uff08kernel buffer\uff09\u4e2d\uff1b<\/p>\n<\/li>\n
    2. \n
      \u7136\u540e\u6570\u636e(kernel buffer)\u62f7\u8d1d\u5230socket buffer\u4e2d\u3002<\/p>\n<\/li>\n
    3. \n
      \u6700\u540e\u5c06socket buffer\u4e2d\u7684\u6570\u636e\u62f7\u8d1d\u5230\u7f51\u5361\u8bbe\u5907\uff08protocol engine\uff09\u4e2d\u4f20\u8f93\uff1b
      \u8fd9\u663e\u7136\u662f\u4e00\u4e2a\u4f1f\u5927\u7684\u8fdb\u6b65\uff1a\u8fd9\u91cc\u628a\u4e0a\u4e0b\u6587\u7684\u5207\u6362\u6b21\u6570\u4ece4\u6b21\u51cf\u5c11\u52302\u6b21\uff0c\u540c\u65f6\u4e5f\u628a\u6570\u636ecopy\u7684\u6b21\u6570\u4ece4\u6b21\u964d\u4f4e\u5230\u4e863\u6b21\u3002<\/p>\n<\/li>\n<\/ol>\n
      \u4f46\u662f\u8fd9\u662fZero-Copy\u4e48\uff0c\u7b54\u6848\u662f\u5426\u5b9a\u7684\u3002<\/p>\n
      \n
      \u8fdb\u9636<\/h2>\n
      Linux 2.1\u5185\u6838\u5f00\u59cb\u5f15\u5165\u4e86sendfile\u51fd\u6570\uff08\u4e0a\u4e00\u8282\u6709\u63d0\u5230\uff09,\u7528\u4e8e\u5c06\u6587\u4ef6\u901a\u8fc7socket\u4f20\u9001\u3002<\/p>\n
      sendfile(socket<\/span>, file, len);
      <\/code><\/pre>\n
      \u8be5\u51fd\u6570\u901a\u8fc7\u4e00\u6b21\u7cfb\u7edf\u8c03\u7528\u5b8c\u6210\u4e86\u6587\u4ef6\u7684\u4f20\u9001\uff0c\u51cf\u5c11\u4e86\u539f\u6765read\/write\u65b9\u5f0f\u7684\u6a21\u5f0f\u5207\u6362\u3002\u6b64\u5916\u66f4\u662f\u51cf\u5c11\u4e86\u6570\u636e\u7684copy, sendfile\u7684\u8be6\u7ec6\u8fc7\u7a0b\u5982\u56fe\uff1a<\/p>\n
      <\/figure>\n
      \u901a\u8fc7sendfile\u4f20\u9001\u6587\u4ef6\u53ea\u9700\u8981\u4e00\u6b21\u7cfb\u7edf\u8c03\u7528\uff0c\u5f53\u8c03\u7528sendfile\u65f6\uff1a<\/section>\n

      \n
        \n
      1. \n
        \u9996\u5148\uff08\u901a\u8fc7DMA\uff09\u5c06\u6570\u636e\u4ece\u78c1\u76d8\u8bfb\u53d6\u5230kernel buffer\u4e2d\uff1b<\/p>\n<\/li>\n
      2. \n
        \u7136\u540e\u5c06kernel buffer\u62f7\u8d1d\u5230socket buffer\u4e2d\uff1b<\/p>\n<\/li>\n
      3. \n
        \u6700\u540e\u5c06socket buffer\u4e2d\u7684\u6570\u636ecopy\u5230\u7f51\u5361\u8bbe\u5907\uff08protocol engine\uff09\u4e2d\u53d1\u9001\uff1b<\/p>\n<\/li>\n<\/ol>\n
        \u8fd9\u4e2a\u8fc7\u7a0b\u5c31\u662f\u7b2c\u4e8c\u8282\uff08\u8be6\u8ff0\uff09\u4e2d\u7684\u90a3\u4e2a\u6b65\u9aa4\u3002<\/p>\n
        sendfile\u4e0eread\/write\u6a21\u5f0f\u76f8\u6bd4\uff0c\u5c11\u4e86\u4e00\u6b21copy\u3002\u4f46\u662f\u4ece\u4e0a\u8ff0\u8fc7\u7a0b\u4e2d\u4e5f\u53ef\u4ee5\u53d1\u73b0\u4ecekernel buffer\u4e2d\u5c06\u6570\u636ecopy\u5230socket buffer\u662f\u6ca1\u6709\u5fc5\u8981\u7684\u3002<\/p>\n
        Linux2.4 \u5185\u6838\u5bf9sendfile\u505a\u4e86\u6539\u8fdb\uff0c\u5982\u56fe\uff1a<\/p>\n
        <\/p>\n
        <\/figure>\n
        \u6539\u8fdb\u540e\u7684\u5904\u7406\u8fc7\u7a0b\u5982\u4e0b\uff1a<\/p>\n
          \n
        1. \n
          \u5c06\u6587\u4ef6\u62f7\u8d1d\u5230kernel buffer\u4e2d\uff1b<\/p>\n<\/li>\n
        2. \n
          \u5411socket buffer\u4e2d\u8ffd\u52a0\u5f53\u524d\u8981\u53d1\u751f\u7684\u6570\u636e\u5728kernel buffer\u4e2d\u7684\u4f4d\u7f6e\u548c\u504f\u79fb\u91cf\uff1b<\/p>\n<\/li>\n
        3. \n
          \u6839\u636esocket buffer\u4e2d\u7684\u4f4d\u7f6e\u548c\u504f\u79fb\u91cf\u76f4\u63a5\u5c06kernel buffer\u7684\u6570\u636ecopy\u5230\u7f51\u5361\u8bbe\u5907\uff08protocol engine\uff09\u4e2d\uff1b<\/p>\n<\/li>\n<\/ol>\n
          \u7ecf\u8fc7\u4e0a\u8ff0\u8fc7\u7a0b\uff0c\u6570\u636e\u53ea\u7ecf\u8fc7\u4e862\u6b21copy\u5c31\u4ece\u78c1\u76d8\u4f20\u9001\u51fa\u53bb\u4e86\u3002\u8fd9\u4e2a\u624d\u662f\u771f\u6b63\u7684Zero-Copy(\u8fd9\u91cc\u7684\u96f6\u62f7\u8d1d\u662f\u9488\u5bf9kernel\u6765\u8bb2\u7684\uff0c\u6570\u636e\u5728kernel\u6a21\u5f0f\u4e0b\u662fZero-Copy)\u3002<\/p>\n
          \u6b63\u662fLinux2.4\u7684\u5185\u6838\u505a\u4e86\u6539\u8fdb\uff0cJava\u4e2d\u7684TransferTo()\u5b9e\u73b0\u4e86Zero-Copy,\u5982\u4e0b\u56fe\uff1a<\/p>\n
          <\/p>\n
          <\/figure>\n
          Zero-Copy\u6280\u672f\u7684\u4f7f\u7528\u573a\u666f\u6709\u5f88\u591a\uff0c\u6bd4\u5982Kafka, \u53c8\u6216\u8005\u662fNetty\u7b49\uff0c\u53ef\u4ee5\u5927\u5927\u63d0\u5347\u7a0b\u5e8f\u7684\u6027\u80fd\u3002<\/p>\n<\/section>","protected":false},"excerpt":{"rendered":"
          \u88c5\u8f7d\u81ea\uff1ahttps:\/\/mp.weixin.qq.com\/s?__biz=MzU0MzQ5MDA0M …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"series":[],"class_list":["post-444","post","type-post","status-publish","format-standard","hentry","category-programmers"],"_links":{"self":[{"href":"https:\/\/fick707.com\/index.php?rest_route=\/wp\/v2\/posts\/444"}],"collection":[{"href":"https:\/\/fick707.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fick707.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fick707.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fick707.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=444"}],"version-history":[{"count":1,"href":"https:\/\/fick707.com\/index.php?rest_route=\/wp\/v2\/posts\/444\/revisions"}],"predecessor-version":[{"id":445,"href":"https:\/\/fick707.com\/index.php?rest_route=\/wp\/v2\/posts\/444\/revisions\/445"}],"wp:attachment":[{"href":"https:\/\/fick707.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=444"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fick707.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=444"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fick707.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=444"},{"taxonomy":"series","embeddable":true,"href":"https:\/\/fick707.com\/index.php?rest_route=%2Fwp%2Fv2%2Fseries&post=444"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}