On Wed, Sep 01, 2010 at 02:22:31AM +0200, Michael Monnerie wrote: > On Mittwoch, 1. September 2010 Dave Chinner wrote: > > You're probably getting RMW cycles on inode writeback. I've been > > noticing this lately with my benchmarking - the VM is being _very > > aggressive_ reclaiming page cache pages vs inode caches and as a > > result the inode buffers used for IO are being reclaimed between the > > time it takes to create the inodes and when they are written back. > > Hence you get lots of reads occurring during inode writeback. > > > > By issuing a sync, you clear out all the inode writeback and all the > > RMW cycles go away. As a result, there is more disk throughput > > availble for the unlink processes. There is a good chance this is > > the case as the number of reads after the sync drop by an order of > > magnitude... > > Nice explanation. > > > > Now it can be that the sync just causes more writes and stalls > > > reads so overall it's slower, but I'm wondering why none of the > > > devices says "100% util", which should be the case on deletes? Or > > > is this again the "mistake" of the utilization calculation that > > > writes do not really show up there? > > > > You're probably CPU bound, not IO bound. > > This is a hexa-core AMD Phenom(tm) II X6 1090T Processor with up to > 3.2GHz per core, so that shouldn't be I'm getting a 8core/16thread server being CPU bound with multithreaded unlink workloads using delaylog, so it's entirely possible that all CPU cores are fully utilised on your machine. > - or is there only one core used? > I think I read somewhere that each AG should get a core or so... If all the files are in one AG, then it will serialise on the AGI header and won't use much more than one CPU. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
