| Message ID | 87k1kyowdf.fsf@notabene.neil.brown.name (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | locks: fix performance regressions. | expand |
Hi, On Wed, Nov 28, 2018 at 11:53:48AM +1100, NeilBrown wrote: > > The kernel test robot reported two performance regressions > caused by recent patches. > Both appear to related to the global spinlock blocked_lock_lock > being taken more often. > > This patch avoids taking that lock in the cases tested. > > Reported-by: kernel test robot <rong.a.chen@intel.com> > Signed-off-by: NeilBrown <neilb@suse.com> > --- > > Hi Jeff, > you might like to merge these back into the patches that introduced > the problem. > Or you might like me to re-send the series with these merged in, > in which case, please ask. > > And a BIG thank-you to the kernel-test-robot team!! > > Thanks, > NeilBrown > > fs/locks.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/fs/locks.c b/fs/locks.c > index f456cd3d9d50..67519a43e27a 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -444,6 +444,13 @@ static void locks_move_blocks(struct file_lock *new, struct file_lock *fl) > { > struct file_lock *f; > > + /* > + * As ctx->flc_lock is held, new requests cannot be added to > + * ->fl_blocked_requests, so we don't need a lock to check if it > + * is empty. > + */ > + if (list_empty(&fl->fl_blocked_requests)) > + return; > spin_lock(&blocked_lock_lock); > list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests); > list_for_each_entry(f, &fl->fl_blocked_requests, fl_blocked_member) > @@ -749,6 +756,20 @@ int locks_delete_block(struct file_lock *waiter) > { > int status = -ENOENT; > > + /* > + * If fl_blocker is NULL, it won't be set again as this thread > + * "owns" the lock and is the only one that might try to claim > + * the lock. So it is safe to test fl_blocker locklessly. > + * Also if fl_blocker is NULL, this waiter is not listed on > + * fl_blocked_requests for some lock, so no other request can > + * be added to the list of fl_blocked_requests for this > + * request. So if fl_blocker is NULL, it is safe to > + * locklessly check if fl_blocked_requests is empty. If both > + * of these checks succeed, there is no need to take the lock. > + */ > + if (waiter->fl_blocker == NULL && > + list_empty(&waiter->fl_blocked_requests)) > + return status; > spin_lock(&blocked_lock_lock); > if (waiter->fl_blocker) > status = 0; > -- > 2.14.0.rc0.dirty > FYI, the performance recovered back, we didn't find any regression between the two commits. commit: 48a7a13ff3 ("locks: use properly initialized file_lock when unlocking.") 8f64e497be ("locks: fix performance regressions.") 48a7a13ff31f0728 8f64e497be9929a2d5904c39c4 ---------------- -------------------------- %stddev change %stddev \ | \ 33.56 ± 3% 5% 35.30 boot-time.boot 10497 ± 3% 12% 11733 ± 4% proc-vmstat.nr_shmem 67392 68449 proc-vmstat.nr_zone_active_anon 67392 68449 proc-vmstat.nr_active_anon 16303 16206 proc-vmstat.nr_slab_reclaimable 30602 29921 proc-vmstat.nr_slab_unreclaimable 0 9e+03 9009 ± 80% latency_stats.avg.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_do_create.nfs3_proc_create.nfs_create.path_openat.do_filp_open.do_sys_open.do_syscall_64 0 6e+03 5837 ±139% latency_stats.avg.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_lookup.nfs_lookup.path_openat.do_filp_open.do_sys_open.do_syscall_64.entry_SYSCALL_64_after_hwframe 149 ± 17% 5e+03 5457 ±137% latency_stats.avg.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_getattr.__nfs_revalidate_inode.nfs_do_access.nfs_permission.inode_permission.link_path_walk.path_lookupat 175 ± 29% 4e+03 3807 ±136% latency_stats.avg.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_lookup.nfs_lookup.__lookup_slow.lookup_slow.walk_component.path_lookupat.filename_lookup 52868 ±110% -4e+04 17482 ± 4% latency_stats.avg.max 45055 ±141% -5e+04 0 latency_stats.avg.io_schedule.nfs_lock_and_join_requests.nfs_updatepage.nfs_write_end.generic_perform_write.nfs_file_write.__vfs_write.vfs_write.ksys_write.do_syscall_64.entry_SYSCALL_64_after_hwframe 227 ± 10% 1e+04 9907 ±136% latency_stats.max.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_getattr.__nfs_revalidate_inode.nfs_do_access.nfs_permission.inode_permission.link_path_walk.path_lookupat 0 9e+03 9367 ± 78% latency_stats.max.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_do_create.nfs3_proc_create.nfs_create.path_openat.do_filp_open.do_sys_open.do_syscall_64 0 6e+03 5837 ±139% latency_stats.max.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_lookup.nfs_lookup.path_openat.do_filp_open.do_sys_open.do_syscall_64.entry_SYSCALL_64_after_hwframe 175 ± 29% 4e+03 3807 ±136% latency_stats.max.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_lookup.nfs_lookup.__lookup_slow.lookup_slow.walk_component.path_lookupat.filename_lookup 98043 ±124% -8e+04 20999 ± 27% latency_stats.max.max 90059 ±141% -9e+04 0 latency_stats.max.io_schedule.nfs_lock_and_join_requests.nfs_updatepage.nfs_write_end.generic_perform_write.nfs_file_write.__vfs_write.vfs_write.ksys_write.do_syscall_64.entry_SYSCALL_64_after_hwframe 1251 ± 23% 5e+04 49005 ±137% latency_stats.sum.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_getattr.__nfs_revalidate_inode.nfs_do_access.nfs_permission.inode_permission.link_path_walk.path_lookupat 0 1e+04 12061 ± 70% latency_stats.sum.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_do_create.nfs3_proc_create.nfs_create.path_openat.do_filp_open.do_sys_open.do_syscall_64 0 6e+03 5837 ±139% latency_stats.sum.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_lookup.nfs_lookup.path_openat.do_filp_open.do_sys_open.do_syscall_64.entry_SYSCALL_64_after_hwframe 175 ± 29% 4e+03 3807 ±136% latency_stats.sum.rpc_wait_bit_killable.__rpc_execute.rpc_run_task.rpc_call_sync.nfs3_rpc_wrapper.nfs3_proc_lookup.nfs_lookup.__lookup_slow.lookup_slow.walk_component.path_lookupat.filename_lookup 90111 ±141% -9e+04 0 latency_stats.sum.io_schedule.nfs_lock_and_join_requests.nfs_updatepage.nfs_write_end.generic_perform_write.nfs_file_write.__vfs_write.vfs_write.ksys_write.do_syscall_64.entry_SYSCALL_64_after_hwframe Best Regards, Rong Chen
On Wed, 2018-11-28 at 11:53 +1100, NeilBrown wrote: > The kernel test robot reported two performance regressions > caused by recent patches. > Both appear to related to the global spinlock blocked_lock_lock > being taken more often. > > This patch avoids taking that lock in the cases tested. > > Reported-by: kernel test robot <rong.a.chen@intel.com> > Signed-off-by: NeilBrown <neilb@suse.com> > --- > > Hi Jeff, > you might like to merge these back into the patches that introduced > the problem. > Or you might like me to re-send the series with these merged in, > in which case, please ask. > Thanks Neil, This looks great. I'll go ahead and toss this patch on top of the pile in linux-next for now. Would you mind resending the series with this patch merged in? I took a quick stab at squashing it into the earlier patch, but there is some churn in this area. Maybe you can also turn that Reported-by: into a Tested-by: in the changelog afterward? > And a BIG thank-you to the kernel-test-robot team!! > Absolutely! We love you guys! > Thanks, > NeilBrown > > fs/locks.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/fs/locks.c b/fs/locks.c > index f456cd3d9d50..67519a43e27a 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -444,6 +444,13 @@ static void locks_move_blocks(struct file_lock *new, struct file_lock *fl) > { > struct file_lock *f; > > + /* > + * As ctx->flc_lock is held, new requests cannot be added to > + * ->fl_blocked_requests, so we don't need a lock to check if it > + * is empty. > + */ > + if (list_empty(&fl->fl_blocked_requests)) > + return; > spin_lock(&blocked_lock_lock); > list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests); > list_for_each_entry(f, &fl->fl_blocked_requests, fl_blocked_member) > @@ -749,6 +756,20 @@ int locks_delete_block(struct file_lock *waiter) > { > int status = -ENOENT; > > + /* > + * If fl_blocker is NULL, it won't be set again as this thread > + * "owns" the lock and is the only one that might try to claim > + * the lock. So it is safe to test fl_blocker locklessly. > + * Also if fl_blocker is NULL, this waiter is not listed on > + * fl_blocked_requests for some lock, so no other request can > + * be added to the list of fl_blocked_requests for this > + * request. So if fl_blocker is NULL, it is safe to > + * locklessly check if fl_blocked_requests is empty. If both > + * of these checks succeed, there is no need to take the lock. > + */ > + if (waiter->fl_blocker == NULL && > + list_empty(&waiter->fl_blocked_requests)) > + return status; > spin_lock(&blocked_lock_lock); > if (waiter->fl_blocker) > status = 0;
diff --git a/fs/locks.c b/fs/locks.c index f456cd3d9d50..67519a43e27a 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -444,6 +444,13 @@ static void locks_move_blocks(struct file_lock *new, struct file_lock *fl) { struct file_lock *f; + /* + * As ctx->flc_lock is held, new requests cannot be added to + * ->fl_blocked_requests, so we don't need a lock to check if it + * is empty. + */ + if (list_empty(&fl->fl_blocked_requests)) + return; spin_lock(&blocked_lock_lock); list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests); list_for_each_entry(f, &fl->fl_blocked_requests, fl_blocked_member) @@ -749,6 +756,20 @@ int locks_delete_block(struct file_lock *waiter) { int status = -ENOENT; + /* + * If fl_blocker is NULL, it won't be set again as this thread + * "owns" the lock and is the only one that might try to claim + * the lock. So it is safe to test fl_blocker locklessly. + * Also if fl_blocker is NULL, this waiter is not listed on + * fl_blocked_requests for some lock, so no other request can + * be added to the list of fl_blocked_requests for this + * request. So if fl_blocker is NULL, it is safe to + * locklessly check if fl_blocked_requests is empty. If both + * of these checks succeed, there is no need to take the lock. + */ + if (waiter->fl_blocker == NULL && + list_empty(&waiter->fl_blocked_requests)) + return status; spin_lock(&blocked_lock_lock); if (waiter->fl_blocker) status = 0;
The kernel test robot reported two performance regressions caused by recent patches. Both appear to related to the global spinlock blocked_lock_lock being taken more often. This patch avoids taking that lock in the cases tested. Reported-by: kernel test robot <rong.a.chen@intel.com> Signed-off-by: NeilBrown <neilb@suse.com> --- Hi Jeff, you might like to merge these back into the patches that introduced the problem. Or you might like me to re-send the series with these merged in, in which case, please ask. And a BIG thank-you to the kernel-test-robot team!! Thanks, NeilBrown fs/locks.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+)