On Monday November 15 2010, Bogdan Cristea wrote:
Hi
I intend to use openSUSE for a real time application which requires to write from memory to hard disk 330 MB of data continuously in about 2.56 s. When I write only 330 MB, the write time using Round Robin real-time scheduler is about 1.5 s, almost two times better than using the default scheduler. If I use 10 times 330 MB data and then I average the write time I get about 7 s regardless of the scheduling policy. My first thought is that the disk defragmentation should be held responsible for such performance penalty. Is this the right explanation ? Are there ways to improve the write time when dealing with large amounts of data ?
The CPU scheduling is probably not the primary issue. The short burst is completing more quickly because the data is simply being transferred to the in-memory disk sector cache. Once you overflow that cache (with the long burst), the kernel is forced to wait for physical I/O operations to complete so those cache blocks can be reassigned to new data from your application.
Bogdan Cristea
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