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net: psample: allow using rate as probability

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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>
This commit is contained in:
Adrian Moreno 2024-07-04 10:56:55 +02:00 committed by Jakub Kicinski
parent c35d86a230
commit 7b1b2b60c6
3 changed files with 14 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/net/psample.h
View File

@ -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;
};

10
include/uapi/linux/psample.h
View File

@ -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
};

3
net/psample/psample.c
View File

@ -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);