On my Duron 1000, Linux 2.4, creating 1.000.000 ACLs and discarding them: empty ACL: 4.48user 0.03system 0:04.50elapsed 100%CPU from text: 13.87user 0.09system 0:13.97elapsed 99%CPU XFS, file: 14.17user 14.95system 0:29.13elapsed 99%CPU creating a list from the entries of an ACL: no entries: 3.86user 0.01system 0:03.86elapsed 100%CPU 6 entries: 16.39user 0.00system 0:16.38elapsed 100%CPU As you can see, creating from file is the longest (as expected). More than half time when creating from file was in kernel mode. In freebsd 4.6, UNDER VMWARE!!!!, same machine: empty ACL: 3.409u 0.432s 0:03.85 99.4% 516+15695k 0+0io 0pf+0w from text: 10.672u 1.016s 0:11.71 99.7% 508+24230k 0+0io 0pf+0w Interesting results, it seems from text is faster here - but here the library doens't support editing, so maybe that's why.