Hi, I have a couple of questions regarding the mmap ioengine. One of the benefits of doing mmap() VS write() is bypassing the need of an intermediate buffer. Instead of preparing a buffer for write(), data can be written directly to file with mmap(). I want to do some performance comparisons on this subject with fio on different filesystems. After reviewing the code a bit, I saw that the mmap ioengine is only responsible for writing the data. The buffer preparation is done in the common code the same way for all ioengines. Am I understanding this correctly? Is there another way to circumvent the buffer filling and implement writing data directly with mmap? Another question relates to mmap and the 'time_based' fio parameter. I want to see how mmap behaves for repeated random access where the initial page fault has less impact. But I would like the repeats be on the workset and not on individual accesses (i.e. write randomly to file, then write again with the same pattern). This is because I do want to see TLB misses on repeated access but not page faults. I tried running fio with --time_based --runtime=<big enough to ensure several repeats>. I saw that indeed the workset was repeated but the results didn't make sense. So again, I reviewed the code and saw that the mmap ioengine will munmap() between each iteration of the workset, which in turn will cause a page fault on each repeated access. Was I wrong to use 'time_based' parameter for this scenario? Does it make any sense to add a parameter for the mmap ioengine not to munmap between iterations? or do something else? I apologize for the lengthy descriptions, Thanks in advance, Yigal -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
