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Date: Mon, 10 Mar 2014 10:58:56 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: John Fastabend <john.fastabend@...il.com>
Cc: xiyou.wangcong@...il.com, jhs@...atatu.com, netdev@...r.kernel.org,
davem@...emloft.net
Subject: Re: [RCU PATCH 09/14] net: sched: make cls_u32 lockless
On Mon, 2014-03-10 at 10:07 -0700, John Fastabend wrote:
> Make cls_u32 classifier safe to run without holding lock. This patch
> converts statistics that are kept in read section u32_classify into
> per cpu counters.
>
> This patch was tested with a tight u32 filter add/delete loop while
> generating traffic with pktgen. By running pktgen on vlan devices
> created on top of a physical device we can hit the qdisc layer
> correctly. For ingress qdisc's a loopback cable was used.
>
> for i in {1..100}; do
> q=`echo $i%8|bc`;
> echo -n "u32 tos: iteration $i on queue $q";
> tc filter add dev p3p2 parent $p prio $i u32 match ip tos 0x10 0xff \
> action skbedit queue_mapping $q;
> sleep 1;
> tc filter del dev p3p2 prio $i;
>
> echo -n "u32 tos hash table: iteration $i on queue $q";
> tc filter add dev p3p2 parent $p protocol ip prio $i handle 628: u32 divisor 1
> tc filter add dev p3p2 parent $p protocol ip prio $i u32 \
> match ip protocol 17 0xff link 628: offset at 0 mask 0xf00 shift 6 plus 0
> tc filter add dev p3p2 parent $p protocol ip prio $i u32 \
> ht 628:0 match ip tos 0x10 0xff action skbedit queue_mapping $q
> sleep 2;
> tc filter del dev p3p2 prio $i
> sleep 1;
> done
>
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
> net/sched/cls_u32.c | 257 +++++++++++++++++++++++++++++++++------------------
> 1 file changed, 168 insertions(+), 89 deletions(-)
>
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 84c28da..e1f7119 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -36,6 +36,7 @@
> #include <linux/kernel.h>
> #include <linux/string.h>
> #include <linux/errno.h>
> +#include <linux/percpu.h>
> #include <linux/rtnetlink.h>
> #include <linux/skbuff.h>
> #include <net/netlink.h>
> @@ -43,40 +44,46 @@
> #include <net/pkt_cls.h>
>
> struct tc_u_knode {
> - struct tc_u_knode *next;
> + struct tc_u_knode __rcu *next;
> u32 handle;
> - struct tc_u_hnode *ht_up;
> + struct tc_u_hnode __rcu *ht_up;
> struct tcf_exts exts;
> #ifdef CONFIG_NET_CLS_IND
> int ifindex;
> #endif
> u8 fshift;
> struct tcf_result res;
> - struct tc_u_hnode *ht_down;
> + struct tc_u_hnode __rcu *ht_down;
> #ifdef CONFIG_CLS_U32_PERF
> - struct tc_u32_pcnt *pf;
> + struct tc_u32_pcnt __percpu *pf;
> #endif
> #ifdef CONFIG_CLS_U32_MARK
> - struct tc_u32_mark mark;
> + u32 val;
> + u32 mask;
> + u32 __percpu *pcpu_success;
> #endif
> + struct tcf_proto *tp;
> + struct rcu_head rcu;
> struct tc_u32_sel sel;
> };
>
> struct tc_u_hnode {
> - struct tc_u_hnode *next;
> + struct tc_u_hnode __rcu *next;
> u32 handle;
> u32 prio;
> struct tc_u_common *tp_c;
> int refcnt;
> unsigned int divisor;
> - struct tc_u_knode *ht[1];
> + struct tc_u_knode __rcu *ht[1];
> + struct rcu_head rcu;
> };
>
> struct tc_u_common {
> - struct tc_u_hnode *hlist;
> + struct tc_u_hnode __rcu *hlist;
> struct Qdisc *q;
> int refcnt;
> u32 hgenerator;
> + struct rcu_head rcu;
> };
>
> static inline unsigned int u32_hash_fold(__be32 key,
> @@ -95,7 +102,7 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp, struct
> unsigned int off;
> } stack[TC_U32_MAXDEPTH];
>
> - struct tc_u_hnode *ht = tp->root;
> + struct tc_u_hnode *ht = rcu_dereference_bh(tp->root);
> unsigned int off = skb_network_offset(skb);
> struct tc_u_knode *n;
> int sdepth = 0;
> @@ -103,27 +110,31 @@ static int u32_classify(struct sk_buff *skb, const struct tcf_proto *tp, struct
> int sel = 0;
> #ifdef CONFIG_CLS_U32_PERF
> int j;
> + struct tc_u32_pcnt *pf;
> #endif
> int i, r;
>
> next_ht:
> - n = ht->ht[sel];
> + n = rcu_dereference_bh(ht->ht[sel]);
>
> next_knode:
> if (n) {
> struct tc_u32_key *key = n->sel.keys;
>
> #ifdef CONFIG_CLS_U32_PERF
> - n->pf->rcnt += 1;
> + pf = this_cpu_ptr(n->pf);
> + pf->rcnt += 1;
Please prefer this_cpu_add() or this_cpu_inc()
> j = 0;
> #endif
>
> #ifdef CONFIG_CLS_U32_MARK
> - if ((skb->mark & n->mark.mask) != n->mark.val) {
> - n = n->next;
> + if ((skb->mark & n->mask) != n->val) {
> + n = rcu_dereference_bh(n->next);
> goto next_knode;
> } else {
> - n->mark.success++;
> + u32 *success = this_cpu_ptr(n->pcpu_success);
> +
> + *success = *success + 1;
Same here, this_cpu_add() or this_cpu_inc()
> }
> #endif
>
> @@ -138,37 +149,41 @@ next_knode:
> if (!data)
> goto out;
> if ((*data ^ key->val) & key->mask) {
> - n = n->next;
> + n = rcu_dereference_bh(n->next);
> goto next_knode;
> }
> #ifdef CONFIG_CLS_U32_PERF
> - n->pf->kcnts[j] += 1;
> + pf = this_cpu_ptr(n->pf);
> + pf->kcnts[j] += 1;
same here.
> j++;
> #endif
> }
> - if (n->ht_down == NULL) {
> +
> + ht = rcu_dereference_bh(n->ht_down);
> + if (!ht) {
> check_terminal:
> if (n->sel.flags & TC_U32_TERMINAL) {
>
> *res = n->res;
> #ifdef CONFIG_NET_CLS_IND
> if (!tcf_match_indev(skb, n->ifindex)) {
> - n = n->next;
> + n = rcu_dereference_bh(n->next);
> goto next_knode;
> }
> #endif
> #ifdef CONFIG_CLS_U32_PERF
> - n->pf->rhit += 1;
> + pf = this_cpu_ptr(n->pf);
> + pf->rhit += 1;
same
Otherwise, patch looks good, thanks !
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