72a9a6ded9
Using a benchmark which has 32 threads creating 2 million files in the same directory, on a machine with 16 CPU cores, I observed poor performance. I noticed that dmu_tx_hold_zap() was using about 30% of all CPU, and doing dnode_hold() 7 times on the same object (the ZAP object that is being held). dmu_tx_hold_zap() keeps a hold on the dnode_t the entire time it is running, in dmu_tx_hold_t:txh_dnode, so it would be nice to use the dnode_t that we already have in hand, rather than repeatedly calling dnode_hold(). To do this, we need to pass the dnode_t down through all the intermediate calls that dmu_tx_hold_zap() makes, making these routines take the dnode_t* rather than an objset_t* and a uint64_t object number. In particular, the following routines will need to have analogous *_by_dnode() variants created: dmu_buf_hold_noread() dmu_buf_hold() zap_lookup() zap_lookup_norm() zap_count_write() zap_lockdir() zap_count_write() This can improve performance on the benchmark described above by 100%, from 30,000 file creations per second to 60,000. (This improvement is on top of that provided by working around the object allocation issue. Peak performance of ~90,000 creations per second was observed with 8 CPUs; adding CPUs past that decreased performance due to lock contention.) The CPU used by dmu_tx_hold_zap() was reduced by 88%, from 340 CPU-seconds to 40 CPU-seconds. Sponsored by: Intel Corp. Closes #109 Reviewed by: Steve Gonczi <steve.gonczi@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com> Reviewed by: Ned Bass <bass6@llnl.gov> Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov> Author: Matthew Ahrens <mahrens@delphix.com> openzfs/openzfs@d3e523d489