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When an interrupt has been handled, the OS notifies the interrupt controller with a EOI sequence. On a POWER9 system using the XIVE interrupt controller, this can be done with a load or a store operation on the ESB interrupt management page of the interrupt. The StoreEOI operation has less latency and improves interrupt handling performance but it was deactivated during the POWER9 DD2.0 timeframe because of ordering issues. We use the LoadEOI today but we plan to reactivate StoreEOI in future architectures. There is usually no need to enforce ordering between ESB load and store operations as they should lead to the same result. E.g. a store trigger and a load EOI can be executed in any order. Assuming the interrupt state is PQ=10, a store trigger followed by a load EOI will return a Q bit. In the reverse order, it will create a new interrupt trigger from HW. In both cases, the handler processing interrupts is notified. In some cases, the XIVE_ESB_SET_PQ_10 load operation is used to disable temporarily the interrupt source (mask/unmask). When the source is reenabled, the OS can detect if interrupts were received while the source was disabled and reinject them. This process needs special care when StoreEOI is activated. The ESB load and store operations should be correctly ordered because a XIVE_ESB_STORE_EOI operation could leave the source enabled if it has not completed before the loads. For those cases, we enforce Load-after-Store ordering with a special load operation offset. To avoid performance impact, this ordering is only enforced when really needed, that is when interrupt sources are temporarily disabled with the XIVE_ESB_SET_PQ_10 load. It should not be needed for other loads. Signed-off-by: Cédric Le Goater <clg@kaod.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200220081506.31209-1-clg@kaod.org |
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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.