497cc00224
When using short intervals e.g. below one millisecond, large packets won't be transmitted at all. The software implementations checks whether the packet can be fit into the remaining interval. Therefore, it takes the packet length and the transmission speed into account. That is correct. However, for large packets it may be that the transmission time exceeds the interval resulting in no packet transmission. The same situation works fine with hardware offloading applied. The problem has been observed with the following schedule and iperf3: |tc qdisc replace dev lan1 parent root handle 100 taprio \ | num_tc 8 \ | map 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 \ | queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \ | base-time $base \ | sched-entry S 0x40 500000 \ | sched-entry S 0xbf 500000 \ | clockid CLOCK_TAI \ | flags 0x00 [...] |root@tsn:~# iperf3 -c 192.168.2.105 |Connecting to host 192.168.2.105, port 5201 |[ 5] local 192.168.2.121 port 52610 connected to 192.168.2.105 port 5201 |[ ID] Interval Transfer Bitrate Retr Cwnd |[ 5] 0.00-1.00 sec 45.2 KBytes 370 Kbits/sec 0 1.41 KBytes |[ 5] 1.00-2.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes After debugging, it seems that the packet length stored in the SKB is about 7000-8000 bytes. Using a 100 Mbit/s link the transmission time is about 600us which larger than the interval of 500us. Therefore, segment the SKB into smaller chunks if the packet is too big. This yields similar results than the hardware offload: |root@tsn:~# iperf3 -c 192.168.2.105 |Connecting to host 192.168.2.105, port 5201 |- - - - - - - - - - - - - - - - - - - - - - - - - |[ ID] Interval Transfer Bitrate Retr |[ 5] 0.00-10.00 sec 48.9 MBytes 41.0 Mbits/sec 0 sender |[ 5] 0.00-10.02 sec 48.7 MBytes 40.7 Mbits/sec receiver Furthermore, the segmentation can be skipped for the full offload case, as the driver or the hardware is expected to handle this. Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.