The struct Qdisc has a lot of holes, especially after commit
a53851e2c321 ("net: sched: explicit locking in gso_cpu fallback"),
which as a side effect, moved the fields just after 'busylock'
on a new cacheline.
Since both 'padded' and 'refcnt' are not updated frequently, and
there is a hole before 'gso_skb', we can move such fields there,
saving a cacheline without any performance side effect.
Before this commit:
pahole -C Qdisc net/sche/sch_generic.o
# ...
/* size: 384, cachelines: 6, members: 25 */
/* sum members: 236, holes: 3, sum holes: 92 */
/* padding: 56 */
After this commit:
pahole -C Qdisc net/sche/sch_generic.o
# ...
/* size: 320, cachelines: 5, members: 25 */
/* sum members: 236, holes: 2, sum holes: 28 */
/* padding: 56 */
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
include/net/sch_generic.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 98c10a28cd01..827a3711dc68 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -85,6 +85,8 @@ struct Qdisc {
struct net_rate_estimator __rcu *rate_est;
struct gnet_stats_basic_cpu __percpu *cpu_bstats;
struct gnet_stats_queue __percpu *cpu_qstats;
+ int padded;
+ refcount_t refcnt;
/*
* For performance sake on SMP, we put highly modified fields at the end
@@ -97,8 +99,6 @@ struct Qdisc {
unsigned long state;
struct Qdisc *next_sched;
struct sk_buff_head skb_bad_txq;
- int padded;
- refcount_t refcnt;
spinlock_t busylock ____cacheline_aligned_in_smp;
spinlock_t seqlock;
--
2.17.0
