On 2019/12/23 21:26, Marcelo Ricardo Leitner wrote:
On Sun, Dec 22, 2019 at 12:22:24PM +0800, Kevin Kou wrote:
On 2019/12/21 0:17, Marcelo Ricardo Leitner wrote:
On Fri, Dec 20, 2019 at 04:47:03AM +0000, Kevin Kou wrote:
The function sctp_sf_eat_sack_6_2 now performs
the Verification Tag validation, Chunk length validation, Bogu check,
and also the detection of out-of-order SACK based on the RFC2960
Section 6.2 at the beginning, and finally performs the further
processing of SACK. The trace_sctp_probe now triggered before
the above necessary validation and check.
This patch is to do the trace_sctp_probe after the necessary check
and validation to SACK.
Signed-off-by: Kevin Kou <qdkevin.kou@xxxxxxxxx>
---
net/sctp/sm_statefuns.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 42558fa..b4a54df 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -3281,7 +3281,6 @@ enum sctp_disposition sctp_sf_eat_sack_6_2(struct net *net,
struct sctp_sackhdr *sackh;
__u32 ctsn;
- trace_sctp_probe(ep, asoc, chunk);
if (!sctp_vtag_verify(chunk, asoc))
return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -3319,6 +3318,8 @@ enum sctp_disposition sctp_sf_eat_sack_6_2(struct net *net,
if (!TSN_lt(ctsn, asoc->next_tsn))
return sctp_sf_violation_ctsn(net, ep, asoc, type, arg, commands);
+ trace_sctp_probe(ep, asoc, chunk);
+
Moving it here will be after the check against ctsn_ack_point, which
could cause duplicated SACKs to be missed from the log.
As this SCTP trace used to trace the changes of SCTP association state in
response to incoming packets(SACK). It is used for debugging SCTP congestion
control algorithms, so according to the code in include/trace/events/sctp.h,
the trace event mainly focus on congestion related information, and there is
no SACK Chunk related information printed. So it is hard to point out
whether the SACK is duplicate one or not based on this trace event.
I see. Yet, it's quite odd to do debugging of congestion control
algorithms without knowing how many TSNs/bytes are being acked by this
ack, but let's keep that aside for now.
I still can't agree with filtering out based the out-of-order SACK check
(the TSN_lt(ctsn, asoc->ctsn_ack_point) check. That is valuable to
congestion control debugging, because it will likely mean that the
sender is working with fewer acks than it would like/expect.
If you need to filter out them and have a "clean" list of what got in,
then the fix it needs lies in adding support for logging the ctsn in
the trace point itself (similarly to the pr_debug in there) and filter
it on post-processing of the logs.
I don't know how much of UAPI cover probe points. Hopefully we can add
that information without having to create new probe points.
Thanks for your comments, In order to avoid affecting the UAPI, let's
keep the existing print fields at present.
PS: You can invert the check in
if (!TSN_lt(ctsn, asoc->next_tsn))
to
if (TSN_lte(asoc->next_tsn, ctsn))
and move it above, so it is done before the out-of-order check, and
the trace point in between them.
I will make this change and commit another patch.
include/trace/events/sctp.h
1. TRACE_EVENT(sctp_probe,
TP_printk("asoc=%#llx mark=%#x bind_port=%d peer_port=%d pathmtu=%d "
"rwnd=%u unack_data=%d",
__entry->asoc, __entry->mark, __entry->bind_port,
__entry->peer_port, __entry->pathmtu, __entry->rwnd,
__entry->unack_data)
2. TRACE_EVENT(sctp_probe_path,
TP_printk("asoc=%#llx%s ipaddr=%pISpc state=%u cwnd=%u ssthresh=%u "
"flight_size=%u partial_bytes_acked=%u pathmtu=%u",
__entry->asoc, __entry->primary ? "(*)" : "",
__entry->ipaddr, __entry->state, __entry->cwnd,
__entry->ssthresh, __entry->flight_size,
__entry->partial_bytes_acked, __entry->pathmtu)
Yes, from the sender-side CC we don't care about it (yet), but it
helps to spot probably avoidable retransmissions.
I think this is cleaning up the noise too much. I can agree with
moving it to after the chunk sanity tests, though.
/* Return this SACK for further processing. */
sctp_add_cmd_sf(commands, SCTP_CMD_PROCESS_SACK, SCTP_CHUNK(chunk));
--
1.8.3.1
