From: Oleg Nesterov last_qsctr is used in rcu_check_quiescent_state() exclusively. We can reset qsctr at the start of the grace period, and then just test qsctr against 0. It is safe because the whole rcu_data is cpu-local, and local timer interrupt checks in_softirq() before incrementing ->qsctr. Also, removes stale comment in rcu_check_quiescent_state(). Signed-off-by: Oleg Nesterov Signed-off-by: Andrew Morton --- 25-akpm/include/linux/rcupdate.h | 2 -- 25-akpm/kernel/rcupdate.c | 11 +++-------- 2 files changed, 3 insertions(+), 10 deletions(-) diff -puN include/linux/rcupdate.h~rcu-eliminate-rcu_datalast_qsctr include/linux/rcupdate.h --- 25/include/linux/rcupdate.h~rcu-eliminate-rcu_datalast_qsctr Mon Nov 29 13:05:54 2004 +++ 25-akpm/include/linux/rcupdate.h Mon Nov 29 13:05:54 2004 @@ -88,8 +88,6 @@ struct rcu_data { /* 1) quiescent state handling : */ long quiescbatch; /* Batch # for grace period */ long qsctr; /* User-mode/idle loop etc. */ - long last_qsctr; /* value of qsctr at beginning */ - /* of rcu grace period */ int qs_pending; /* core waits for quiesc state */ /* 2) batch handling */ diff -puN kernel/rcupdate.c~rcu-eliminate-rcu_datalast_qsctr kernel/rcupdate.c --- 25/kernel/rcupdate.c~rcu-eliminate-rcu_datalast_qsctr Mon Nov 29 13:05:54 2004 +++ 25-akpm/kernel/rcupdate.c Mon Nov 29 13:05:54 2004 @@ -219,9 +219,9 @@ static void rcu_check_quiescent_state(st struct rcu_state *rsp, struct rcu_data *rdp) { if (rdp->quiescbatch != rcp->cur) { - /* new grace period: record qsctr value. */ + /* new grace period: reset qsctr value. */ rdp->qs_pending = 1; - rdp->last_qsctr = rdp->qsctr; + rdp->qsctr = 0; rdp->quiescbatch = rcp->cur; return; } @@ -233,12 +233,7 @@ static void rcu_check_quiescent_state(st if (!rdp->qs_pending) return; - /* - * Races with local timer interrupt - in the worst case - * we may miss one quiescent state of that CPU. That is - * tolerable. So no need to disable interrupts. - */ - if (rdp->qsctr == rdp->last_qsctr) + if (rdp->qsctr == 0) return; rdp->qs_pending = 0; _