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The driver calls napi_schedule_irqoff() from a context where, in RT, hardirqs are not disabled, since the IRQ handler is force-threaded. In the call path of this function, __raise_softirq_irqoff() is modifying its per-CPU mask of pending softirqs that must be processed, using or_softirq_pending(). The or_softirq_pending() function is not atomic, but since interrupts are supposed to be disabled, nobody should be preempting it, and the operation should be safe. Nonetheless, when running with hardirqs on, as in the PREEMPT_RT case, it isn't safe, and the pending softirqs mask can get corrupted, resulting in softirqs being lost and never processed. To have common code that works with PREEMPT_RT and with mainline Linux, we can use plain napi_schedule() instead. The difference is that napi_schedule() (via __napi_schedule) also calls local_irq_save, which disables hardirqs if they aren't already. But, since they already are disabled in non-RT, this means that in practice we don't see any measurable difference in throughput or latency with this patch. Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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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.