[PATCH v3 net-next] tc: remove unused redirect ttl

[PATCH v3 net-next] tc: remove unused redirect ttl

[Alexei Starovoitov]

From: Jamal Hadi Salim <jhs@mojatatu.com>

improves ingress+u32 performance from 22.4 Mpps to 22.9 Mpps

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Florian Westphal <fw@strlen.de>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---

V2->V3: added From:Jamal tag and Acks
V1->V2: missed removal of unused variable.

 include/uapi/linux/pkt_cls.h |    2 ++
 net/core/dev.c               |    9 ---------
 2 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/include/uapi/linux/pkt_cls.h b/include/uapi/linux/pkt_cls.h
index bf08e76bf505..f6344a522cd6 100644
--- a/include/uapi/linux/pkt_cls.h
+++ b/include/uapi/linux/pkt_cls.h
@@ -62,11 +62,13 @@ bits 9,10,11: redirect counter -  redirect TTL. Loop avoidance
 #define SET_TC_NCLS(v)   ( TC_NCLS | (v & ~TC_NCLS))
 #define CLR_TC_NCLS(v)   ( v & ~TC_NCLS)
 
+#ifndef __KERNEL__
 #define S_TC_RTTL          _TC_MAKE32(9)
 #define M_TC_RTTL          _TC_MAKEMASK(3,S_TC_RTTL)
 #define G_TC_RTTL(x)       _TC_GETVALUE(x,S_TC_RTTL,M_TC_RTTL)
 #define V_TC_RTTL(x)       _TC_MAKEVALUE(x,S_TC_RTTL)
 #define SET_TC_RTTL(v,n)   ((V_TC_RTTL(n)) | (v & ~M_TC_RTTL))
+#endif
 
 #define S_TC_AT          _TC_MAKE32(12)
 #define M_TC_AT          _TC_MAKEMASK(2,S_TC_AT)
diff --git a/net/core/dev.c b/net/core/dev.c
index c7ba0388f1be..97a15ae8d07a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3531,18 +3531,9 @@ EXPORT_SYMBOL_GPL(br_fdb_test_addr_hook);
  */
 static int ing_filter(struct sk_buff *skb, struct netdev_queue *rxq)
 {
-	struct net_device *dev = skb->dev;
-	u32 ttl = G_TC_RTTL(skb->tc_verd);
 	int result = TC_ACT_OK;
 	struct Qdisc *q;
 
-	if (unlikely(MAX_RED_LOOP < ttl++)) {
-		net_warn_ratelimited("Redir loop detected Dropping packet (%d->%d)\n",
-				     skb->skb_iif, dev->ifindex);
-		return TC_ACT_SHOT;
-	}
-
-	skb->tc_verd = SET_TC_RTTL(skb->tc_verd, ttl);
 	skb->tc_verd = SET_TC_AT(skb->tc_verd, AT_INGRESS);
 
 	q = rcu_dereference(rxq->qdisc);
-- 
1.7.9.5

Re: [PATCH v3 net-next] tc: remove unused redirect ttl

[Jesper Dangaard Brouer]

On Fri,  1 May 2015 22:19:43 -0700
Alexei Starovoitov <ast@plumgrid.com> wrote:

> From: Jamal Hadi Salim <jhs@mojatatu.com>
> 
> improves ingress+u32 performance from 22.4 Mpps to 22.9 Mpps

I like this change and I'm ACKing it.

But I would like to comment on these performance numbers.  I assume this
is a single CPU test with your pktgen RX/STACK_INJECT mode that drops
the packet "early (in ip_rcv() I think).

It sound impressive to get +0.5 Mpps improvement from such a small
change, while in reality this is approx a 1ns improvement.

 (1/(22.4*10^6)*10^9) = 44.64ns
 (1/(22.9*10^6)*10^9) = 43.67ns
 improvement diff     =  0.97ns

I'm a fan of zooming in on parts of the stack, as it allow us to
performance optimize and measure parts of the stack that is normally
hard to measure. And your ingress use-case is valid.  People should
just be aware, that we can easily "over-sell" when "zooming" in...


> Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
> Acked-by: Florian Westphal <fw@strlen.de>
> Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

Re: [PATCH v3 net-next] tc: remove unused redirect ttl

[David Miller]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Fri,  1 May 2015 22:19:43 -0700

> From: Jamal Hadi Salim <jhs@mojatatu.com>
> 
> improves ingress+u32 performance from 22.4 Mpps to 22.9 Mpps
> 
> Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
> Acked-by: Florian Westphal <fw@strlen.de>
> Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Applied, thanks.