On Thu, Sep 06, 2007 at 10:58:40AM +0200, Mark Hlawatschek wrote: > Hi, > > during a performance analysis and tuning session, I did some profiling with > oprofile on GFS and dlm. > I got some weird results ... > > The installed software is: > RHEL4u5, kernel 2.6.9-55.0.2.ELsmp > GFS: 2.6.9-72.2.0.2 > DLM: 2.6.9-46.16.0.1 > > The configuration includes 2 clusternodes. > > I put the following load on one cluster node: > > 100 processes are doing in parallel: > - create 1000 files with 100kb size each (ie altogether we have 100.000 files) > - flock 1000 files > - unlink 1000 files. > > The following oprofile output shows, that the system spends about 49% > (75%*65%*) of the time in gfs_unlinked_get. > Looking into the code whe can see, that this is related to unlinked.c: > 53 9394211 58.7081 : ul = list_entry(tmp, struct > gfs_unlinked, ul_list); > > It can also be observed, that dlm spends more than 50% of its time in > searching for hashes... > > Is this the expected behaviour or can this be tuned somewhere ? Thanks for doing this, it's very interesting. For the dlm search_hashchain, could you try changing rsbtbl_size to 1024 (the default is 256). echo 1024 > /proc/.../rsbtbl_size after loading the dlm module, but before the lockspace is created. For gfs, I haven't looked very closely, but the linked list could probably be simply turned into a hash table. We'd want to study it more closely to make sure that the long non-hashed list is really the right thing to fix (i.e. we don't want to just fix a symptom of something else). Dave -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
