On Mon, Nov 23, 2009 at 01:51:05PM -0500, tytso@xxxxxxx wrote: > Now, all of this having been said, Feodra 11 and 12 have been using > ext4 as the default filesystem, and for generic desktop usage, people > haven't been screaming about the increased CPU overhead implied by > engaging the jbd2 machinery on every sys_write(). > > However, we have had a report that some enterprise database developers > have noticed the increased overhead in ext4, and this is on our list > of things that require some performance tuning. Hence my comments > about a mount option to adjust s_time_gran for the benefit of database > workloads, and once we have that moun option, since enabling i_version > would mean once again needing to update the inode at every single > write(2) call, we would be back with the same problem. > > Maybe we can find a way to be more clever about doing some (but not > all) of the jbd2 work on each sys_write(), and deferring as much as > possible to the commit handling. We need to do some investigating to > see if that's possible. Even if it isn't, though, my gut tells me > that we will probably be able to enable i_version by default for > desktop workloads, and tell database server folks that they should > mount with the mount options "noi_version,time_gran=1s", or some such. > > I'd like to do some testing to confirm my intuition first, of course, > but that's how I'm currently leaning. Does that make sense? I think so, thanks. So do I have this todo list approximately right?: 1. Use an atomic type instead of a spinlock for i_version, and do some before-and-after benchmarking of writes (following your suggestions in http://marc.info/?l=linux-ext4&m=125900130605891&w=2) 2. Turn on i_version by default. (At this point it shouldn't be making things any worse than the high-resolution timestamps are.) 3. Find someone to run database benchmarks, and work on noi_version,time_gran=1s (or whatever) options for their case. I wish I could volunteer at least for #1, but embarassingly don't have much more than dual-core machines lying around right now to test with. --b. -- 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
