netdev - [PATCH v2 net-next 3/7] net_sched: act: make tcfg

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Message-Id: <1436164896-8243-5-git-send-email-edumazet@google.com>
Date:	Sun,  5 Jul 2015 23:41:29 -0700
From:	Eric Dumazet <edumazet@...gle.com>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	John Fastabend <john.fastabend@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Eric Dumazet <edumazet@...il.com>
Subject: [PATCH v2 net-next 3/7] net_sched: act: make tcfg_pval non zero

First step for gact RCU operation :

Instead of testing if tcfg_pval is zero or not, just make it 1.

No change in behavior, but slightly faster code.

The smp_rmb()/smp_wmb() barriers, while not strictly needed at this
stage are added for upcoming spinlock removal.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Alexei Starovoitov <ast@...mgrid.com>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
Acked-by: John Fastabend <john.fastabend@...il.com>
---
 net/sched/act_gact.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/sched/act_gact.c b/net/sched/act_gact.c
index a4f8af29ee30..22a3a61aa090 100644
--- a/net/sched/act_gact.c
+++ b/net/sched/act_gact.c
@@ -28,14 +28,16 @@
 #ifdef CONFIG_GACT_PROB
 static int gact_net_rand(struct tcf_gact *gact)
 {
-	if (!gact->tcfg_pval || prandom_u32() % gact->tcfg_pval)
+	smp_rmb(); /* coupled with smp_wmb() in tcf_gact_init() */
+	if (prandom_u32() % gact->tcfg_pval)
 		return gact->tcf_action;
 	return gact->tcfg_paction;
 }
 
 static int gact_determ(struct tcf_gact *gact)
 {
-	if (!gact->tcfg_pval || gact->tcf_bstats.packets % gact->tcfg_pval)
+	smp_rmb(); /* coupled with smp_wmb() in tcf_gact_init() */
+	if (gact->tcf_bstats.packets % gact->tcfg_pval)
 		return gact->tcf_action;
 	return gact->tcfg_paction;
 }
@@ -105,7 +107,11 @@ static int tcf_gact_init(struct net *net, struct nlattr *nla,
 #ifdef CONFIG_GACT_PROB
 	if (p_parm) {
 		gact->tcfg_paction = p_parm->paction;
-		gact->tcfg_pval    = p_parm->pval;
+		gact->tcfg_pval    = max_t(u16, 1, p_parm->pval);
+		/* Make sure tcfg_pval is written before tcfg_ptype
+		 * coupled with smp_rmb() in gact_net_rand() & gact_determ()
+		 */
+		smp_wmb();
 		gact->tcfg_ptype   = p_parm->ptype;
 	}
 #endif
-- 
2.4.3.573.g4eafbef

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