On Fri, Dec 25, 2009 at 02:46:31AM +0300, Evgeniy Polyakov wrote: > > [1] http://samba.org/ftp/tridge/dbench/README > > Was not able to resist to write a small notice, what no matter what, but > whatever benchmark is running, it _does_ show system behaviour in one > or another condition. And when system behaves rather badly, it is quite > a common comment, that benchmark was useless. But it did show that > system has a problem, even if rarely triggered one :) If people are using benchmarks to improve file system, and a benchmark shows a problem, then trying to remedy the performance issue is a good thing to do, of course. Sometimes, though the case which is demonstrated by a poor benchmark is an extremely rare corner case that doesn't accurately reflect common real-life workloads --- and if addressing it results in a tradeoff which degrades much more common real-life situations, then that would be a bad thing. In situations where benchmarks are used competitively, it's rare that it's actually a *problem*. Instead it's much more common that a developer is trying to prove that their file system is *better* to gullible users who think that a single one-dimentional number is enough for them to chose file system X over file system Y. For example, if I wanted to play that game and tell people that ext4 is better, I'd might pick this graph: http://btrfs.boxacle.net/repository/single-disk/2.6.29-rc2/2.6.29-rc2/2.6.29-rc2_Mail_server_simulation._num_threads=32.html On the other hand, this one shows ext4 as the worst compared to all other file systems: http://btrfs.boxacle.net/repository/single-disk/2.6.29-rc2/2.6.29-rc2/2.6.29-rc2_Large_file_random_writes_odirect._num_threads=8.html Benchmarking, like statistics, can be extremely deceptive, and if people do things like carefully order a tar file so the files are optimal for a file system, it's fair to ask whether that's a common thing for people to be doing (either unpacking tarballs or unpacking tarballs whose files have been carefully ordered for a particular file systems). When it's the only number used by a file system developer when trying to convince users they should use their file system, at least in my humble opinion it becomes murderously dishonest. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
