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srcu: Reduce scans of srcu_data in counter wrap check

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Currently, given a multi-level srcu_node tree, SRCU can scan the full
set of srcu_data structures at each level when cleaning up after a grace
period.  This, though harmless otherwise, represents pointless overhead.
This commit therefore eliminates this overhead by scanning the srcu_data
structures only when traversing the leaf srcu_node structures.

Signed-off-by: Ildar Ismagilov <devix84@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Ildar Ismagilov 2018-01-31 22:42:21 +03:00 committed by Paul E. McKenney
parent a35d13ec36
commit 8ddbd8832d
1 changed files with 4 additions and 2 deletions
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6
kernel/rcu/srcutree.c
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@ -527,6 +527,7 @@ static void srcu_gp_end(struct srcu_struct *sp)
{ {
unsigned long cbdelay; unsigned long cbdelay;
bool cbs; bool cbs;
bool last_lvl;
int cpu; int cpu;
unsigned long flags; unsigned long flags;
unsigned long gpseq; unsigned long gpseq;
@ -559,7 +560,8 @@ static void srcu_gp_end(struct srcu_struct *sp)
rcu_for_each_node_breadth_first(sp, snp) { rcu_for_each_node_breadth_first(sp, snp) {
spin_lock_irq_rcu_node(snp); spin_lock_irq_rcu_node(snp);
cbs = false; cbs = false;
if (snp >= sp->level[rcu_num_lvls - 1]) last_lvl = snp >= sp->level[rcu_num_lvls - 1];
if (last_lvl)
cbs = snp->srcu_have_cbs[idx] == gpseq; cbs = snp->srcu_have_cbs[idx] == gpseq;
snp->srcu_have_cbs[idx] = gpseq; snp->srcu_have_cbs[idx] = gpseq;
rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
@ -572,7 +574,7 @@ static void srcu_gp_end(struct srcu_struct *sp)
srcu_schedule_cbs_snp(sp, snp, mask, cbdelay); srcu_schedule_cbs_snp(sp, snp, mask, cbdelay);
/* Occasionally prevent srcu_data counter wrap. */ /* Occasionally prevent srcu_data counter wrap. */
if (!(gpseq & counter_wrap_check)) if (!(gpseq & counter_wrap_check) && last_lvl)
for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) { for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
sdp = per_cpu_ptr(sp->sda, cpu); sdp = per_cpu_ptr(sp->sda, cpu);
spin_lock_irqsave_rcu_node(sdp, flags); spin_lock_irqsave_rcu_node(sdp, flags);