外文翻譯--網絡性能的測量-wenkub
2023-05-19 06:02:52 本頁面
【正文】 c. 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 kernel and added to the transmission queue. If there is sufficient buffer space, timing 1000 UDP calls does not mean that all the data have been sent. Most of them may still be in the kernel, but the performance utility thinks they have all been transmitted. Understand What You Are Measuring When you measure the time to read a remote file, your measurements depend on the work, the operating systems on both the client and server, the particular hardware interface boards used, their drivers, and other factors. If the measurements are done carefully, you will ultimately discover the file transfer time for the configuration you are using. If your goal is to tune this particular configuration, these measurements are fine. However, if you are making similar measurements on three different systems in order to choose which work interface board to buy, your results could be thrown off pletely by the fact that one
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