RE: [RFC/PATCH net-next v3 5/8] flow_offload: add process to update action stats from hardware

On October 30, 2021 1:11 AM, Vlad Buslov [off-list ref] wrote:

On Thu 28 Oct 2021 at 14:06, Simon Horman [off-list ref]
wrote:

quoted

From: Baowen Zheng <redacted>

When collecting stats for actions update them using both both hardware
and software counters.

Stats update process should not in context of preempt_disable.

I think you are missing a word here.

Thanks, we will fix it in next patch.

quoted

Signed-off-by: Baowen Zheng <redacted>
Signed-off-by: Louis Peens <redacted>
Signed-off-by: Simon Horman <redacted>
---
 include/net/act_api.h |  1 +
 include/net/pkt_cls.h | 18 ++++++++++--------
 net/sched/act_api.c   | 37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/include/net/act_api.h b/include/net/act_api.h index

671208bd27ef..80a9d1e7d805 100644

--- a/include/net/act_api.h
+++ b/include/net/act_api.h

@@ -247,6 +247,7 @@ void tcf_action_update_stats(struct tc_action *a,

u64 bytes, u64 packets,

quoted

 			     u64 drops, bool hw);
 int tcf_action_copy_stats(struct sk_buff *, struct tc_action *, int);
int tcf_action_offload_del(struct tc_action *action);
+int tcf_action_update_hw_stats(struct tc_action *action);
 int tcf_action_check_ctrlact(int action, struct tcf_proto *tp,
 			     struct tcf_chain **handle,
 			     struct netlink_ext_ack *newchain); diff --git
a/include/net/pkt_cls.h b/include/net/pkt_cls.h index
44ae5182a965..88788b821f76 100644

--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h

@@ -292,18 +292,20 @@ tcf_exts_stats_update(const struct tcf_exts

*exts,  #ifdef CONFIG_NET_CLS_ACT
 	int i;

-	preempt_disable();
-
 	for (i = 0; i < exts->nr_actions; i++) {
 		struct tc_action *a = exts->actions[i];

-		tcf_action_stats_update(a, bytes, packets, drops,
-					lastuse, true);
-		a->used_hw_stats = used_hw_stats;
-		a->used_hw_stats_valid = used_hw_stats_valid;
-	}
+		/* if stats from hw, just skip */
+		if (tcf_action_update_hw_stats(a)) {
+			preempt_disable();
+			tcf_action_stats_update(a, bytes, packets, drops,
+						lastuse, true);
+			preempt_enable();

-	preempt_enable();
+			a->used_hw_stats = used_hw_stats;
+			a->used_hw_stats_valid = used_hw_stats_valid;
+		}
+	}
 #endif
 }

diff --git a/net/sched/act_api.c b/net/sched/act_api.c index

604bf1923bcc..881c7ba4d180 100644

--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c

@@ -1238,6 +1238,40 @@ static int tcf_action_offload_add(struct tc_action

*action,

quoted

 	return err;
 }

+int tcf_action_update_hw_stats(struct tc_action *action) {
+	struct flow_offload_action fl_act = {};
+	int err = 0;
+
+	if (!tc_act_in_hw(action))
+		return -EOPNOTSUPP;
+
+	err = flow_action_init(&fl_act, action, FLOW_ACT_STATS, NULL);
+	if (err)
+		goto err_out;
+
+	err = tcf_action_offload_cmd(&fl_act, NULL, NULL);
+
+	if (!err && fl_act.stats.lastused) {
+		preempt_disable();
+		tcf_action_stats_update(action, fl_act.stats.bytes,
+					fl_act.stats.pkts,
+					fl_act.stats.drops,
+					fl_act.stats.lastused,
+					true);
+		preempt_enable();
+		action->used_hw_stats = fl_act.stats.used_hw_stats;
+		action->used_hw_stats_valid = true;
+		err = 0;

Error handling here is slightly convoluted. This line assigns err=0 third time (it is
initialized with zero and then we can only get here if result of
tcf_action_offload_cmd() assigned 'err' to zero again).
Considering that error handler in this function is empty we can just return
errors directly as soon as they happen and return zero at the end of the
function.

Thanks, we will change as your suggestion.

quoted

+	} else {
+		err = -EOPNOTSUPP;

Hmm the code can return error here when tcf_action_offload_cmd()
succeeded but 'lastused' is zero. Such behavior will cause
tcf_exts_stats_update() to update action with filter counter values. Is this the
desired behavior when, for example, in filter action list there is and action that
can drop packets followed by some shared action? In such case 'lastused' can
be zero if all packets that filter matched were dropped by previous action and
shared action will be assigned with filter counter value that includes dropped
packets/bytes.

Thanks, we will consider if it make sense to only judge return value err from tcf_action_offload_cmd.

quoted

+	}
+
+err_out:
+	return err;
+}
+EXPORT_SYMBOL(tcf_action_update_hw_stats);
+
 int tcf_action_offload_del(struct tc_action *action)  {
 	struct flow_offload_action fl_act;

@@ -1362,6 +1396,9 @@ int tcf_action_copy_stats(struct sk_buff *skb,

struct tc_action *p,

quoted

 	if (p == NULL)
 		goto errout;

+	/* update hw stats for this action */
+	tcf_action_update_hw_stats(p);
+
 	/* compat_mode being true specifies a call that is supposed
 	 * to add additional backward compatibility statistic TLVs.
 	 */