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Vladimir Oltean 483f0e3975 net: dsa: sja1105: fix bandwidth discrepancy between tc-cbs software and offload 
[ Upstream commit 954ad9bf13 ]

More careful measurement of the tc-cbs bandwidth shows that the stream
bandwidth (effectively idleslope) increases, there is a larger and
larger discrepancy between the rate limit obtained by the software
Qdisc, and the rate limit obtained by its offloaded counterpart.

The discrepancy becomes so large, that e.g. at an idleslope of 40000
(40Mbps), the offloaded cbs does not actually rate limit anything, and
traffic will pass at line rate through a 100 Mbps port.

The reason for the discrepancy is that the hardware documentation I've
been following is incorrect. UM11040.pdf (for SJA1105P/Q/R/S) states
about IDLE_SLOPE that it is "the rate (in unit of bytes/sec) at which
the credit counter is increased".

Cross-checking with UM10944.pdf (for SJA1105E/T) and UM11107.pdf
(for SJA1110), the wording is different: "This field specifies the
value, in bytes per second times link speed, by which the credit counter
is increased".

So there's an extra scaling for link speed that the driver is currently
not accounting for, and apparently (empirically), that link speed is
expressed in Kbps.

I've pondered whether to pollute the sja1105_mac_link_up()
implementation with CBS shaper reprogramming, but I don't think it is
worth it. IMO, the UAPI exposed by tc-cbs requires user space to
recalculate the sendslope anyway, since the formula for that depends on
port_transmit_rate (see man tc-cbs), which is not an invariant from tc's
perspective.

So we use the offload->sendslope and offload->idleslope to deduce the
original port_transmit_rate from the CBS formula, and use that value to
scale the offload->sendslope and offload->idleslope to values that the
hardware understands.

Some numerical data points:

 40Mbps stream, max interfering frame size 1500, port speed 100M
 ---------------------------------------------------------------

 tc-cbs parameters:
 idleslope 40000 sendslope -60000 locredit -900 hicredit 600

 which result in hardware values:

 Before (doesn't work)           After (works)
 credit_hi    600                600
 credit_lo    900                900
 send_slope   7500000            75
 idle_slope   5000000            50

 40Mbps stream, max interfering frame size 1500, port speed 1G
 -------------------------------------------------------------

 tc-cbs parameters:
 idleslope 40000 sendslope -960000 locredit -1440 hicredit 60

 which result in hardware values:

 Before (doesn't work)           After (works)
 credit_hi    60                 60
 credit_lo    1440               1440
 send_slope   120000000          120
 idle_slope   5000000            5

 5.12Mbps stream, max interfering frame size 1522, port speed 100M
 -----------------------------------------------------------------

 tc-cbs parameters:
 idleslope 5120 sendslope -94880 locredit -1444 hicredit 77

 which result in hardware values:

 Before (doesn't work)           After (works)
 credit_hi    77                 77
 credit_lo    1444               1444
 send_slope   11860000           118
 idle_slope   640000             6

Tested on SJA1105T, SJA1105S and SJA1110A, at 1Gbps and 100Mbps.

Fixes: 4d7525085a ("net: dsa: sja1105: offload the Credit-Based Shaper qdisc")
Reported-by: Yanan Yang <yanan.yang@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-09-19 12:28:03 +02:00
arch x86/virt: Drop unnecessary check on extended CPUID level in cpu_has_svm() 2023-09-19 12:27:59 +02:00
block blk-throttle: consider 'carryover_ios/bytes' in throtl_trim_slice() 2023-09-19 12:28:00 +02:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto X.509: if signature is unsupported skip validation 2023-09-13 09:43:03 +02:00
Documentation dt-bindings: clock: xlnx,versal-clk: drop select:false 2023-09-19 12:27:57 +02:00
drivers net: dsa: sja1105: fix bandwidth discrepancy between tc-cbs software and offload 2023-09-19 12:28:03 +02:00
fs smb: propagate error code of extract_sharename() 2023-09-19 12:28:00 +02:00
include ip_tunnels: use DEV_STATS_INC() 2023-09-19 12:28:03 +02:00
init sched/psi: Select KERNFS as needed 2023-09-13 09:42:28 +02:00
io_uring io_uring: Don't set affinity on a dying sqpoll thread 2023-09-19 12:27:54 +02:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel tracing: Zero the pipe cpumask on alloc to avoid spurious -EBUSY 2023-09-13 09:43:05 +02:00
lib idr: fix param name in idr_alloc_cyclic() doc 2023-09-19 12:28:03 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: hugetlb_vmemmap: fix a race between vmemmap pmd split 2023-09-19 12:27:56 +02:00
net kcm: Destroy mutex in kcm_exit_net() 2023-09-19 12:28:02 +02:00
rust rust: allocator: Prevent mis-aligned allocation 2023-08-11 12:08:18 +02:00
samples samples/bpf: fix broken map lookup probe 2023-09-13 09:42:34 +02:00
scripts kconfig: fix possible buffer overflow 2023-09-19 12:27:59 +02:00
security smackfs: Prevent underflow in smk_set_cipso() 2023-09-13 09:42:42 +02:00
sound ASoC: tegra: Fix SFC conversion for few rates 2023-09-19 12:27:56 +02:00
tools perf test stat_bpf_counters_cgrp: Enhance perf stat cgroup BPF counter test 2023-09-19 12:28:00 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt kvm/vfio: ensure kvg instance stays around in kvm_vfio_group_add() 2023-09-13 09:42:46 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS devlink: move code to a dedicated directory 2023-08-30 16:11:00 +02:00
Makefile kbuild: do not run depmod for 'make modules_sign' 2023-09-19 12:27:58 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.