[lkml]   [2018]   [Feb]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
SubjectRe: [PATCH 2/2] srcu: reduce scans of srcu_data in counter wrap check
On Wed, Jan 31, 2018 at 10:42:21PM +0300, Ildar Ismagilov wrote:
> This patch reduce scans of srcu_data in case of a srcu_struct
> tree have more than one levels

Good catch!!! Applied for testing and review.

I had to hand-apply this patch as well, and also fill out the commit log.
In addition, in the future, please capitalize the word in the Subject
line following the colon (":"). Please see below for the updated commit
and again please let me know if I messed something up.

Thanx, Paul


commit bcec03ee2e43f2a24c61a99709d4dd1aa90438c2
Author: Ildar Ismagilov <>
Date: Wed Jan 31 22:42:21 2018 +0300

srcu: Reduce scans of srcu_data in counter wrap check

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 <>
Signed-off-by: Paul E. McKenney <>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index ad3e1aa5e6ea..72dc6e39be14 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -527,6 +527,7 @@ static void srcu_gp_end(struct srcu_struct *sp)
unsigned long cbdelay;
bool cbs;
+ bool last_lvl;
int cpu;
unsigned long flags;
unsigned long gpseq;
@@ -559,7 +560,8 @@ static void srcu_gp_end(struct srcu_struct *sp)
rcu_for_each_node_breadth_first(sp, snp) {
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;
snp->srcu_have_cbs[idx] = gpseq;
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);

/* 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++) {
sdp = per_cpu_ptr(sp->sda, cpu);
spin_lock_irqsave_rcu_node(sdp, flags);
 \ /
  Last update: 2018-02-03 21:13    [W:0.035 / U:34.040 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site