> When comparing the 2.6.20.15 kernel with the 2.6.25 kernel, > I have noticed that: For the underlying 3ware devices, all > benchmarks -- dd, bonnie++, [ ... ] I get about an 8 percent > DROP in READING performance with the 2.6.25 kernel. It seems particularly dumb to avoid giving absolute numbers here, but yet it is sort of expected from someone thinking that "READING performance" and benchmark results are the same thing (expecially someone who uses bonnie++ and does not give the exact parameters used too). > Does anybody have any insights into what might be going on > here? Does Linux software RAID need to be configured > differently in 2.6.25 to NOT lose READ performance? [ ... ] A difference of 10% plus or minus is insignificant and well within measurement error and happenstance. Some people ascribe significance to such variations, but that is due to lack of understanding, as if a complex and often poorly designed IO subsystem that is meant to distribute iops across several devices had deterministic performance on a multitasking system with load spread over several CPUs. Variations like that can depend on a timing bug being fixed in an unrelated driver. In particular as to MD read performance, it has been reported quite a few times in this mailing list that it seems to depend to a very large extent on the precise value of the block device read ahead, with variations of *several times*, and with best benchmark results achieved by laughably (also because most likely counterproductive) large values of that parameter. Worrying about 8% is pointless and clueless. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
