On Sun, Aug 05, 2018 at 10:31:03PM +0200, Heiner Kallweit wrote: > If flag IRQCHIP_ONESHOT_SAFE isn't set for an irqchip and we have a > threaded interrupt with no primary handler, then flag IRQF_ONESHOT > needs to be set for the interrupt, causing some overhead in the > threaded interrupt handler. For more detailed explanation also check > following comment in __setup_irq(): > > The interrupt was requested with handler = NULL, so we use the default > primary handler for it. But it does not have the oneshot flag set. > In combination with level interrupts this is deadly, because the > default primary handler just wakes the thread, then the irq lines is > reenabled, but the device still has the level irq asserted. > Rinse and repeat.... > While this works for edge type interrupts, we play it safe and reject > unconditionally because we can't say for sure which type this interrupt > really has. The type flags are unreliable as the underlying chip > implementation can override them. > > Another comment in __setup_irq() gives a hint already that this > overhead can be avoided for PCI-MSI: > > Some irq chips like MSI based interrupts are per se one shot safe. > Check the chip flags, so we can avoid the unmask dance at the end > of the threaded handler for those. > > Following this let's mark all PCI-MSI irqchip's as oneshot-safe. > > See also discussion here: > https://marc.info/?l=linux-pci&m=153332526101128&w=2 > > Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx> Applied to pci/msi for v4.19, thanks! > --- > v2: > - extended commit message > --- > drivers/pci/msi.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c > index 4d88afdf..f2ef8964 100644 > --- a/drivers/pci/msi.c > +++ b/drivers/pci/msi.c > @@ -1446,6 +1446,9 @@ struct irq_domain *pci_msi_create_irq_domain(struct fwnode_handle *fwnode, > if (IS_ENABLED(CONFIG_GENERIC_IRQ_RESERVATION_MODE)) > info->flags |= MSI_FLAG_MUST_REACTIVATE; > > + /* PCI-MSI is oneshot-safe */ > + info->chip->flags |= IRQCHIP_ONESHOT_SAFE; > + > domain = msi_create_irq_domain(fwnode, info, parent); > if (!domain) > return NULL; > -- > 2.18.0 > >
