On Wed, Oct 02, 2013 at 12:43:24PM +1000, Michael Ellerman wrote: > On Tue, Oct 01, 2013 at 12:35:27PM +0200, Alexander Gordeev wrote: > > On Tue, Oct 01, 2013 at 05:51:33PM +1000, Michael Ellerman wrote: > > > The disadvantage is that any restriction imposed on us above the quota > > > can only be reported as an error from pci_enable_msix(). > > > > > > The quota code, called from pci_get_msix_limit(), can only do so much to > > > interogate firmware about the limitations. The ultimate way to check if > > > firmware will give us enough MSIs is to try and allocate them. But we > > > can't do that from pci_get_msix_limit() because the driver is not asking > > > us to enable MSIs, just query them. > > > > If things are this way then pci_enable_msix() already exposed to this > > problem internally on pSeries. > > > > I see that even successful quota checks in rtas_msi_check_device() and > > rtas_setup_msi_irqs() do not guarantee (as you say) that firmware will > > give enough MSIs. Hence, pci_enable_msix() might fail even though the > > its quota checks succeeded. > > Yes, but it can report that failure to the caller, which can then retry. If a driver wants to retry after a failure it is up to the driver (but why?). The current guidlines state: "If this function returns a negative number, it indicates an error and the driver should not attempt to allocate any more MSI-X interrupts for this device." Anyway, what number could the driver retry with after it got a negative errno? > > Therefore, nothing will really change if we make pci_get_msix_limit() check > > quota and hope the follow-up call to pci_enable_msix() succeeded. > > No that's not equivalent. Under your scheme if pci_enable_msix() fails > then the caller just bails, it will never try again with a lower number. Currently under the very same circumstances (the quota check within rtas_setup_msi_irqs() returned Q vectors while the firmware has only F vectors to allocate and Q > F) rtas_setup_msi_irqs() fails, pci_enable_msix() fails, the caller bails and never try again with a lower number. Am I missing something here? > cheers -- Regards, Alexander Gordeev agordeev@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
