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In a system with high real-time requirements, the timeout mechanism of ordinary timers with jiffies granularity is insufficient to meet the demands for real-time performance. Meanwhile, the optimization of CPU usage with af_packet is quite significant. Use hrtimer instead of timer to help compensate for the shortcomings in real-time performance. In HZ=100 or HZ=250 system, the update of TP_STATUS_USER is not real-time enough, with fluctuations reaching over 8ms (on a system with HZ=250). This is unacceptable in some high real-time systems that require timely processing of network packets. By replacing it with hrtimer, if a timeout of 2ms is set, the update of TP_STATUS_USER can be stabilized to within 3 ms. Delete delete_blk_timer field, because hrtimer_cancel will check and wait until the timer callback return and ensure never enter callback again. Simplify the logic related to setting timeout, only update the hrtimer expire time within the hrtimer callback, no longer update the expire time in prb_open_block which is called by tpacket_rcv or timer callback. Reasons why NOT update hrtimer in prb_open_block: 1) It will increase complexity to distinguish the two caller scenario. 2) hrtimer_cancel and hrtimer_start need to be called if you want to update TMO of an already enqueued hrtimer, leading to complex shutdown logic. One side effect of NOT update hrtimer when called by tpacket_rcv is that a newly opened block triggered by tpacket_rcv may be retired earlier than expected. On the other hand, if timeout is updated in prb_open_block, the frequent reception of network packets that leads to prb_open_block being called may cause hrtimer to be removed and enqueued repeatedly. The retire hrtimer expiration is unconditional and periodic. If there are numerous packet sockets on the system, please set an appropriate timeout to avoid frequent enqueueing of hrtimers. Reviewed-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com> Reviewed-by: Jason Xing <kerneljasonxing@gmail.com> Link: https://lore.kernel.org/all/20250831100822.1238795-1-jackzxcui1989@163.com/ Signed-off-by: Xin Zhao <jackzxcui1989@163.com> Link: https://patch.msgid.link/20250908104549.204412-3-jackzxcui1989@163.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
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| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
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| Kbuild | ||
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| 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 reStructuredText 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.