[PATCH net-next v8 04/10] net: psample: allow using rate as probability

Adrian Moreno
2024-07-02T09:54:14Z

Although not explicitly documented in the psample module itself, the
definition of PSAMPLE_ATTR_SAMPLE_RATE seems inherited from act_sample.

Quoting tc-sample(8):
"RATE of 100 will lead to an average of one sampled packet out of every
100 observed."

With this semantics, the rates that we can express with an unsigned
32-bits number are very unevenly distributed and concentrated towards
"sampling few packets".
For example, we can express a probability of 2.32E-8% but we
cannot express anything between 100% and 50%.

For sampling applications that are capable of sampling a decent
amount of packets, this sampling rate semantics is not very useful.

Add a new flag to the uAPI that indicates that the sampling rate is
expressed in scaled probability, this is:
- 0 is 0% probability, no packets get sampled.
- U32_MAX is 100% probability, all packets get sampled.

Reviewed-by: Aaron Conole <aconole@redhat.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Adrian Moreno <amorenoz@redhat.com>
---
include/net/psample.h | 3 ++-
include/uapi/linux/psample.h | 10 +++++++++-
net/psample/psample.c | 3 +++
3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/net/psample.h b/include/net/psample.h
index 2ac71260a546..c52e9ebd88dd 100644
--- a/include/net/psample.h
+++ b/include/net/psample.h
@@ -24,7 +24,8 @@ struct psample_metadata {
u8 out_tc_valid:1,
out_tc_occ_valid:1,
latency_valid:1,
- unused:5;
+ rate_as_probability:1,
+ unused:4;
const u8 *user_cookie;
u32 user_cookie_len;
};
diff --git a/include/uapi/linux/psample.h b/include/uapi/linux/psample.h
index e80637e1d97b..b765f0e81f20 100644
--- a/include/uapi/linux/psample.h
+++ b/include/uapi/linux/psample.h
@@ -8,7 +8,11 @@ enum {
PSAMPLE_ATTR_ORIGSIZE,
PSAMPLE_ATTR_SAMPLE_GROUP,
PSAMPLE_ATTR_GROUP_SEQ,
- PSAMPLE_ATTR_SAMPLE_RATE,
+ PSAMPLE_ATTR_SAMPLE_RATE, /* u32, ratio between observed and
+ * sampled packets or scaled probability
+ * if PSAMPLE_ATTR_SAMPLE_PROBABILITY
+ * is set.
+ */
PSAMPLE_ATTR_DATA,
PSAMPLE_ATTR_GROUP_REFCOUNT,
PSAMPLE_ATTR_TUNNEL,
@@ -20,6 +24,10 @@ enum {
PSAMPLE_ATTR_TIMESTAMP, /* u64, nanoseconds */
PSAMPLE_ATTR_PROTO, /* u16 */
PSAMPLE_ATTR_USER_COOKIE, /* binary, user provided data */
+ PSAMPLE_ATTR_SAMPLE_PROBABILITY,/* no argument, interpret rate in
+ * PSAMPLE_ATTR_SAMPLE_RATE as a
+ * probability scaled 0 - U32_MAX.
+ */

__PSAMPLE_ATTR_MAX
};
diff --git a/net/psample/psample.c b/net/psample/psample.c
index 1c76f3e48dcd..f48b5b9cd409 100644
--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -497,6 +497,9 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
md->user_cookie))
goto error;

+ if (md->rate_as_probability)
+ nla_put_flag(skb, PSAMPLE_ATTR_SAMPLE_PROBABILITY);
+
genlmsg_end(nl_skb, data);
genlmsg_multicast_netns(&psample_nl_family, group->net, nl_skb, 0,
PSAMPLE_NL_MCGRP_SAMPLE, GFP_ATOMIC);
--
2.45.2