On Fri, Jun 19, 2015 at 08:40:11AM +0800, cauchy-love wrote: > > the iozone command line is: > ./iozone -i 0 -i 1 -f ./iotmp -Rab ./iotmp.xls -g 8G -n 4G -c > > The problem is why the performance difference is so big for different linux > kernels. The guest's io performance test is by both FTP tools and raw write, > which demonstrate the much lower performance of Centos 7 (1/10 of that on > Centos 6.5). And how can I debug this problem?
You are missing the -I command-line option for O_DIRECT. When you run without -I you are not benchmarking just disk I/O but also page cache performance, which varies depending on the amount of RAM available. This means you cannot compare guest results with host results. Stefan
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