On Tue, Apr 17, 2012 at 01:53:20PM -0500, Eric Sandeen wrote: > > In my (admittedly quick, hacky) test, xfs suffed about a 1% perf > degradation, ext4 about 8%. Until we at least know why ext4 is so > much worse, I'll signal a strong NAK for this change, for whatever > may or may not be worth. :) Was this on a HDD? Try it on a PCIe attached flash device that doesn't support persistent discard. :-) I suspect in that case even with XFS you will see a bigger performance penalty than that. That being said, I agree that it would be good to see if we can improve ext4's performance without the big hammer, regardless of whether or not we can bring the uninit->init overhead down to zero. Some of the overhead I suspect is due the fact that ext4 is doing physical block journalling, which we won't be able to work around, but it may be there is room for improvement in the extent manipulation codepaths and and how they get called from the I/O completion handler. (Oh, and that's assuming you were using DIO or AIO; if you were using buffered writes, you were probably getting hit by the ordered mode flush requirements, since in buffered mode we do the uninit->init conversion before we write out the data block, so we have to do an implicit fsync in the commit transaction. Fixing that is something we've talked about before, and that's certainly worth doing; it requires the I/O tree work that we talked about at the ext4 workshop as a prerequisite, though.) - 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
