net: psample: allow using rate as probability

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>
Link: https://patch.msgid.link/20240704085710.353845-5-amorenoz@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/psample.h b/include/net/psample.h
index 2ac71260a546117e5f8807857065907ec26cf661..c52e9ebd88ddfbc55ada860e02dc399e972f7cd6 100644 (file)
--- 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 e80637e1d97b95579bb4175f98be49fcb8d12496..b765f0e81f20390afb8bae2891b3f718789af4a8 100644 (file)
--- 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 1c76f3e48dcd98fc4f446d63389c2ebe5b6eb6c2..f48b5b9cd409e67646155727454e17a943366e25 100644 (file)
--- 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);