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@xxxxxxxxx>
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
> ---
>
> 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
