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什么是KVM和QEMU
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<h1 id="kvm">KVM</h1>
<p>KVM实际是linux内核提供的虚拟化架构，可将内核直接充当hypervisor来使用。KVM需要处理器硬件本身支持虚拟化扩展，如intel VT 和AMD AMD-V技术。KVM本身不实现任何模拟，仅仅是暴露了一个/dev/kvm接口，这个接口可被宿主机用来主要负责vCPU的创建，虚拟内存的地址空间分配，vCPU寄存器的读写以及vCPU的运行。 有了KVM以后，guest os的CPU指令不用再经过QEMU来转译便可直接运行，大大提高了运行速度。但KVM的kvm.ko本身只提供了CPU和内存的虚拟化，所以它必须结合QEMU才能构成一个完整的虚拟化技术，</p>
<a id="more"></a>
<h1 id="qemu">QEMU</h1>
<p>QEMU是一个主机上的VMM（virtual machine monitor）,通过动态二进制转换来模拟CPU，并提供一系列的硬件模型，使guest os认为自己和硬件直接打交道，其实是同QEMU模拟出来的硬件打交道，QEMU再将这些指令翻译给真正硬件进行操作。 通过这种模式，guest os可以和主机上的硬盘，网卡，CPU，CD-ROM，音频设备和USB设备进行交互。但由于所有指令都需要经过QEMU来翻译，因而性能会比较差：</p>
<p><img src="https://raw.githubusercontent.com/libertyunionkjy/jykeImg/master/images/20200724134422.png" /></p>
<h1 id="qemukvm">QEMU+KVM</h1>
<p>综上QEMU其实可以完整的模拟一台服务器，但是因为guest os的指令都要经过QEMU的翻译才能够执行，所以效率比较低。而KVM是linux内核提供的虚拟化架构，KVM负责cpu虚拟化+内存虚拟化，实现了cpu和内存的虚拟化，但kvm并不能模拟其他设备。还必须有个运行在用户空间的工具才行，KVM的开发者选择了比较成熟的开源虚拟化软件QEMU来作为这个工具，QEMU模拟IO设备（网卡，磁盘等），对其进行了修改，最后形成了QEMU-KVM。KVM加上QEMU后就是完整意义上的服务器虚拟化。</p>
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.then(({ results }) => {
if (results.length > 0) {
var counter = results[0];
leancloudSelector(url).innerText = counter.time + 1;
Counter('put', '/classes/Counter/' + counter.objectId, { time: { '__op': 'Increment', 'amount': 1 } })
.catch(error => {
console.error('Failed to save visitor count', error);
});
} else {
Counter('post', '/classes/Counter', { title, url, time: 1 })
.then(response => response.json())
.then(() => {
leancloudSelector(url).innerText = 1;
})
.catch(error => {
console.error('Failed to create', error);
});
}
})
.catch(error => {
console.error('LeanCloud Counter Error', error);
});
}
function showTime(Counter) {
var visitors = document.querySelectorAll('.leancloud_visitors');
var entries = [...visitors].map(element => {
return decodeURI(element.id);
});
Counter('get', '/classes/Counter?where=' + encodeURIComponent(JSON.stringify({ url: { '$in': entries } })))
.then(response => response.json())
.then(({ results }) => {
for (let url of entries) {
let target = results.find(item => item.url === url);
leancloudSelector(url).innerText = target ? target.time : 0;
}
})
.catch(error => {
console.error('LeanCloud Counter Error', error);
});
}
let { app_id, app_key, server_url } = {"enable":true,"app_id":"LUfk9hhalFl8bvU1sch5iOtc-9Nh9j0Va","app_key":"pI9Q11Bxqxk1Q5eJLKIG1gim","server_url":null,"security":false};
function fetchData(api_server) {
var Counter = (method, url, data) => {
return fetch(`${api_server}/1.1${url}`, {
method,
headers: {
'X-LC-Id' : app_id,
'X-LC-Key' : app_key,
'Content-Type': 'application/json',
},
body: JSON.stringify(data)
});
};
if (CONFIG.page.isPost) {
if (CONFIG.hostname !== location.hostname) return;
addCount(Counter);
} else if (document.querySelectorAll('.post-title-link').length >= 1) {
showTime(Counter);
}
}
let api_server = app_id.slice(-9) !== '-MdYXbMMI' ? server_url : `https://${app_id.slice(0, 8).toLowerCase()}.api.lncldglobal.com`;
if (api_server) {
fetchData(api_server);
} else {
fetch('https://app-router.leancloud.cn/2/route?appId=' + app_id)
.then(response => response.json())
.then(({ api_server }) => {
fetchData('https://' + api_server);
});
}
})();
</script>
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NexT.utils.loadComments(document.querySelector('#valine-comments'), () => {
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new Valine(Object.assign({
el : '#valine-comments',
path : location.pathname,
}, {"enable":true,"appId":"tnKOKDSuvxOLRFeojycmFGDV-MdYXbMMI","appKey":"Q4ro4ajDoVK1ScWWSlGCxY3G","notify":true,"verify":false,"placeholder":"快来评论吧！柯柯给你举高高ヽ(✿ﾟ▽ﾟ)ノ","avatar":"monsterid","meta":["nick","mail","link"],"pageSize":10,"language":"zh-cn","visitor":false,"comment_count":true,"recordIP":false,"serverURLs":null}
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