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The per-CPU statistics (struct fc_stats) is updated by getting a stable per-CPU pointer via get_cpu() + per_cpu_ptr() and then performing the increment. This can be optimized by using this_cpu_*() which will do whatever is needed on the architecture to perform the update safe and efficient. The read out of the individual value (fc_get_host_stats()) should be done by using READ_ONCE() instead of a plain-C access. The difference is that READ_ONCE() will always perform a single access while the plain-C access can be split by the compiler into two loads if it appears beneficial. The usage of u64 has the side-effect that it is also 64bit wide on 32bit architectures and the read is always split into two loads. The can lead to strange values if the read happens during an update which alters both 32bit parts of the 64bit value. This can be circumvented by either using a 32bit variables on 32bit architecures or extending the statistics with a sequence counter. Use this_cpu_*() API to update the statistics and READ_ONCE() to read it. Link: https://lore.kernel.org/r/20220506105758.283887-3-bigeasy@linutronix.de Reviewed-by: Davidlohr Bueso <dave@stgolabs.net> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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.