So it's upstream with kernel v6.6-rc6.
With that it affects jammy, lunar and mantic.
(Would have been ideal to have it tagged as upstream stable update.)
** Also affects: linux (Ubuntu Jammy)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Mantic)
Importance: Undecided
Assignee: Skipper Bug Screeners (skipper-screen-team)
Status: New
** Also affects: linux (Ubuntu Lunar)
Importance: Undecided
Status: New
** Also affects: ubuntu-z-systems
Importance: Undecided
Status: New
** Changed in: ubuntu-z-systems
Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)
** Changed in: linux (Ubuntu Mantic)
Assignee: Skipper Bug Screeners (skipper-screen-team) => (unassigned)
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https://bugs.launchpad.net/bugs/2039575
Title:
[UBUNTU 22.04] SMC stats: Wrong bucket calculation for payload of
exactly 4096 bytes.
Status in Ubuntu on IBM z Systems:
New
Status in linux package in Ubuntu:
New
Status in linux source package in Jammy:
New
Status in linux source package in Lunar:
New
Status in linux source package in Mantic:
New
Bug description:
Bug description by Nils H.:
------------
Overview:
------------
The following line in the SMC stats code (net/smc/smc_stats.h) caught my
attention when using a payload of exactly 4096 bytes:
#define SMC_STAT_PAYLOAD_SUB(_smc_stats, _tech, key, _len, _rc) \
do { \
typeof(_smc_stats) stats = (_smc_stats); \
typeof(_tech) t = (_tech); \
typeof(_len) l = (_len); \
int _pos = fls64((l) >> 13); \
typeof(_rc) r = (_rc); \
int m = SMC_BUF_MAX - 1; \
this_cpu_inc((*stats).smc[t].key ## _cnt); \
if (r <= 0) \
break; \
_pos = (_pos < m) ? ((l == 1 << (_pos + 12)) ? _pos - 1 : _pos) : m; \
<---
this_cpu_inc((*stats).smc[t].key ## _pd.buf[_pos]); \
this_cpu_add((*stats).smc[t].key ## _bytes, r); \
} \
while (0)
With l = 4096, _pos evaluates to -1.
Checking with the following uperf profile:
# cat rr1c-4kx4k---1.xml
<?xml version="1.0"?>
<profile name="TCP_RR">
<group nprocs="1">
<!--group nthreads="1"-->
<!-- if we want to run processes -->
<!--group nprocs="1"-->
<transaction iterations="1">
<flowop type="connect" options="remotehost=<remote IP>
protocol=tcp tcp_nodelay" />
</transaction>
<transaction iterations="1">
<flowop type="write" options="size=4096"/>
<flowop type="read" options="size=4096"/>
</transaction>
<transaction iterations="1">
<flowop type="disconnect" />
</transaction>
</group>
</profile>
smcd stats output:
# smcd -d stats reset
SMC-D Connections Summary
Total connections handled 2
SMC connections 2 (client 2, server 0)
v1 0
v2 2
Handshake errors 0 (client 0, server 0)
Avg requests per SMC conn 14.0
TCP fallback 0 (client 0, server 0)
RX Stats
Data transmitted (Bytes) 5796 (5.796K)
Total requests 9
Buffer full 0 (0.00%)
Buffer downgrades 0
Buffer reuses 0
8KB 16KB 32KB 64KB 128KB 256KB 512KB >512KB
Bufs 0 0 0 2 0 0 0 1
Reqs 8 0 0 0 0 0 0 0
TX Stats
Data transmitted (Bytes) 9960 (9.960K)
Total requests 19
Buffer full 0 (0.00%)
Buffer full (remote) 0 (0.00%)
Buffer too small 0 (0.00%)
Buffer too small (remote) 0 (0.00%)
Buffer downgrades 0
Buffer reuses 0
8KB 16KB 32KB 64KB 128KB 256KB 512KB >512KB
Bufs 0 2 0 0 0 0 0 0
Reqs 18 0 0 0 0 0 0 1
Extras
Special socket calls 0
cork 0
nodelay 0
sendpage 0
splice 0
urgent data 0
Instead of including the payload in the wrong >512KB buckets, output should
be to have 19 reqs in the 8KB buckets for TX stats and 9 reqs in the 8KB bucket
for RX stats.
--------
Repro:
--------
0. Install uperf.
1. Reset SMC-D stats on client and server.
2. Start uperf at server side: "uperf -vs".
3. Update profile with remote IP (server IP) and start uperf at client:
"uperf -vai 5 -m rr1c-4kx4k---1.xml" (uperf profile, see above)
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