Commit 7b1b2b60 authored by Adrian Moreno's avatar Adrian Moreno Committed by Jakub Kicinski
Browse files

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: default avatarAaron Conole <aconole@redhat.com>
Acked-by: default avatarEelco Chaudron <echaudro@redhat.com>
Reviewed-by: default avatarIdo Schimmel <idosch@nvidia.com>
Signed-off-by: default avatarAdrian Moreno <amorenoz@redhat.com>
Link: https://patch.msgid.link/20240704085710.353845-5-amorenoz@redhat.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent c35d86a2

include/net/psample.h

+2 −1
Original line number Diff line number Diff line
@@ -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;

};

include/uapi/linux/psample.h

+9 −1
Original line number Diff line number Diff line
@@ -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

};

net/psample/psample.c

+3 −0
Original line number Diff line number Diff line
@@ -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);