Commit-ID: 13dc7d0c7a2ed438f0ec8e9fb365a1256d87cf87 Gitweb: https://git.kernel.org/tip/13dc7d0c7a2ed438f0ec8e9fb365a1256d87cf87 Author: Zhang, Jun <jun.zh...@intel.com> AuthorDate: Wed, 19 Dec 2018 10:37:34 -0800 Committer: Paul E. McKenney <paul...@linux.ibm.com> CommitDate: Fri, 25 Jan 2019 15:30:00 -0800
rcu: Prevent needless ->gp_seq_needed update in __note_gp_changes() Currently, __note_gp_changes() checks to see if the rcu_node structure's ->gp_seq_needed is greater than or equal to that of the rcu_data structure, and if so, updates the rcu_data structure's ->gp_seq_needed field. This results in a useless store in the case where the two fields are equal. This commit therefore carries out this store only in the case where the rcu_node structure's ->gp_seq_needed is strictly greater than that of the rcu_data structure. Signed-off-by: "Zhang, Jun" <jun.zh...@intel.com> Signed-off-by: Paul E. McKenney <paul...@linux.ibm.com> Link: https://lkml.kernel.org/r/88dc34334ca3444c85d647dbfa962c2735ad5...@shsmsx104.ccr.corp.intel.com --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 21775eebb8f0..9d0e2ac9356e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1758,7 +1758,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) zero_cpu_stall_ticks(rdp); } rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ - if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap) + if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) rdp->gp_seq_needed = rnp->gp_seq_needed; WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp);
