外文翻译--网络性能的测量(编辑修改稿)

外文翻译--网络性能的测量(编辑修改稿)内容摘要：

in may give different results than if made the next day. Likewise, if some researcher has decided to run a video conference over your work during your tests, you may get a biased result. It is best to run tests on an idle system and create the entire workload yourself. Even this approach has pitfalls though. While you might think nobody will be using the work at 3 ., that might be precisely when the automatic backup program begins copying all the disks to tape. Furthermore, there might be heavy traffic for your wonderful World Wide Web pages from distant time zones. Caching Can Wreak Havoc with Measurements The obvious way to measure file transfer times is to open a large file, read the whole thing, close it, and see how long it takes. Then repeat the measurement many more times to get a good average. The trouble is, the system may cache the file, so only the first measurement actually involves work traffic. The rest are just reads from the local cache. The results from such a measurement are essentially worthless (unless you want to measure cache performance). Often you can get around caching by simply overflowing the cache. For example, if the cache is 10 MB, the test loop could open, read, and close two 10MB files on each pass, in an attempt to force the cache hit rate to 0. Still, caution is advised unless you are absolutely sure you understand the caching algorithm. Buffering can have a similar effect. One popular TCP/IP performance utility program has been known to report that UDP can achieve a performance substantially higher than the physical line allows. How does this occur? A call to UDP normally returns control as soon as the message has been accepted by the k。