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The not-per-CPU variant of qdisc tc (traffic control) statistics, Qdisc::gnet_stats_basic_packed bstats, is protected with Qdisc::running sequence counter. This sequence counter is used for reliably protecting bstats reads from parallel writes. Meanwhile, the seqcount's write section covers a much wider area than bstats update: qdisc_run_begin() => qdisc_run_end(). That read/write section asymmetry can lead to needless retries of the read section. To prepare for removing the Qdisc::running sequence counter altogether, introduce a u64_stats sync point inside bstats instead. Modify _bstats_update() to start/end the bstats u64_stats write section. For bisectability, and finer commits granularity, the bstats read section is still protected with a Qdisc::running read/retry loop and qdisc_run_begin/end() still starts/ends that seqcount write section. Once all call sites are modified to use _bstats_update(), the Qdisc::running seqcount will be removed and bstats read/retry loop will be modified to utilize the internal u64_stats sync point. Note, using u64_stats implies no sequence counter protection for 64-bit architectures. This can lead to the statistics "packets" vs. "bytes" values getting out of sync on rare occasions. The individual values will still be valid. [bigeasy: Minor commit message edits, init all gnet_stats_basic_packed.] Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: David S. Miller <davem@davemloft.net>
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.