Messages in this thread | | | Date | Sun, 29 Mar 2009 21:55:59 -0600 | Subject | Re: Linux 2.6.29 | From | "Trenton D. Adams" <> |
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On Sun, Mar 29, 2009 at 9:28 PM, Theodore Tso <tytso@mit.edu> wrote: > On Sun, Mar 29, 2009 at 07:29:09PM -0600, Trenton Adams wrote: >> I am slightly confused by the "data=ordered" thing that everyone is >> mentioning of late. In theory, it made sense to me before I tried it. >> I switched to mounting my ext3 as ext4, and I'm still seeing >> seriously delayed fsyncs. Theodore, I used a modified version of your >> fsync-tester.c to bench 1M writes, while doing a dd, and I'm still >> getting *almost* as bad of "fsync" performance as I was on ext3. On >> ext3, the fsync would usually not finish until the dd was complete. > > How much memory do you have? On my 4gig X61 laptop, using a 5400 rpm > laptop drive, I see typical times of 1 to 1.5 seconds, with a few > outliers at 4-5 seconds. With ext3, the fsync times immediately > jumped up to 6-8 seconds, with the outliers in the 13-15 second range.
2G, and I believe 5400rpm
> > (This is with a filesystem formated as ext3, and mounted as either > ext3 or ext4; if the filesystem is formatted using "mke2fs -t ext4", > what you see is a very smooth 1.2-1.5 seconds fsync latency, indirect > blocks for very big files end up being quite inefficient.)
Oh. I thought I had read somewhere that mounting ext4 over ext3 would solve the problem. Not sure where I read that now. Sorry for wasting your time.
> > So I'm seeing a definite difference --- but also please remember that > "dd if=/dev/zero of=bigzero.img" really is an unfair, worst-case > scenario, since you are dirtying memory as fast as your CPU will dirty > pages. Normally, even if you are running distcc, the rate at which > you can dirty pages will be throttled at your local network speed.
Yes, I realize that. When trying to find performance problems I try to be as *unfair* as possible. :D
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