+0
−6
Loading
knfsd: remove unreported filehandle stats counters
The file nfsfh.c contains two static variables nfsd_nr_verified and nfsd_nr_put. These are counters which are incremented as a side effect of the fh_verify() fh_compose() and fh_put() operations, i.e. at least twice per NFS call for any non-trivial workload. Needless to say this makes the cacheline that contains them (and any other innocent victims) a very hot contention point indeed under high call-rate workloads on multiprocessor NFS server. It also turns out that these counters are not used anywhere. They're not reported to userspace, they're not used in logic, they're not even exported from the object file (let alone the module). All they do is waste CPU time. So this patch removes them. Tests on a 16 CPU Altix A4700 with 2 10gige Myricom cards, configured separately (no bonding). Workload is 640 client threads doing directory traverals with random small reads, from server RAM. Before ====== Kernel profile: % cumulative self self total time samples samples calls 1/call 1/call name 6.05 2716.00 2716.00 30406 0.09 1.02 svc_process 4.44 4706.00 1990.00 1975 1.01 1.01 spin_unlock_irqrestore 3.72 6376.00 1670.00 1666 1.00 1.00 svc_export_put 3.41 7907.00 1531.00 1786 0.86 1.02 nfsd_ofcache_lookup 3.25 9363.00 1456.00 10965 0.13 1.01 nfsd_dispatch 3.10 10752.00 1389.00 1376 1.01 1.01 nfsd_cache_lookup 2.57 11907.00 1155.00 4517 0.26 1.03 svc_tcp_recvfrom ... 2.21 15352.00 1003.00 1081 0.93 1.00 nfsd_choose_ofc <---- ^^^^ Here the function nfsd_choose_ofc() reads a global variable which by accident happened to be located in the same cacheline as nfsd_nr_verified. Call rate: nullarbor:~ # pmdumptext nfs3.server.calls ... Thu Dec 13 00:15:27 184780.663 Thu Dec 13 00:15:28 184885.881 Thu Dec 13 00:15:29 184449.215 Thu Dec 13 00:15:30 184971.058 Thu Dec 13 00:15:31 185036.052 Thu Dec 13 00:15:32 185250.475 Thu Dec 13 00:15:33 184481.319 Thu Dec 13 00:15:34 185225.737 Thu Dec 13 00:15:35 185408.018 Thu Dec 13 00:15:36 185335.764 After ===== kernel profile: % cumulative self self total time samples samples calls 1/call 1/call name 6.33 2813.00 2813.00 29979 0.09 1.01 svc_process 4.66 4883.00 2070.00 2065 1.00 1.00 spin_unlock_irqrestore 4.06 6687.00 1804.00 2182 0.83 1.00 nfsd_ofcache_lookup 3.20 8110.00 1423.00 10932 0.13 1.00 nfsd_dispatch 3.03 9456.00 1346.00 1343 1.00 1.00 nfsd_cache_lookup 2.62 10622.00 1166.00 4645 0.25 1.01 svc_tcp_recvfrom [...] 0.10 42586.00 44.00 74 0.59 1.00 nfsd_choose_ofc <--- HA!! ^^^^ Call rate: nullarbor:~ # pmdumptext nfs3.server.calls ... Thu Dec 13 01:45:28 194677.118 Thu Dec 13 01:45:29 193932.692 Thu Dec 13 01:45:30 194294.364 Thu Dec 13 01:45:31 194971.276 Thu Dec 13 01:45:32 194111.207 Thu Dec 13 01:45:33 194999.635 Thu Dec 13 01:45:34 195312.594 Thu Dec 13 01:45:35 195707.293 Thu Dec 13 01:45:36 194610.353 Thu Dec 13 01:45:37 195913.662 Thu Dec 13 01:45:38 194808.675 i.e. about a 5.3% improvement in call rate. Signed-off-by:Greg Banks <gnb@melbourne.sgi.com> Reviewed-by: