On Thu, 2020-02-20 at 08:15:06 UTC, =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= wrote: > 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 <c...@kaod.org>
Applied to powerpc topic/ppc-kvm, thanks. https://git.kernel.org/powerpc/c/b1f9be9392f090f08e4ad9e2c68963aeff03bd67 cheers
