On 27/10/2015 07:35, Yunhong Jiang wrote: > On Mon, Oct 26, 2015 at 09:37:14PM -0600, Alex Williamson wrote: >> On Mon, 2015-10-26 at 18:20 -0700, Yunhong Jiang wrote: >>> An option to force VFIO PCI MSI/MSI-X handler as non-threaded IRQ, >>> even when CONFIG_IRQ_FORCED_THREADING=y. This is uselful when >>> assigning a device to a guest with low latency requirement since it >>> reduce the context switch to/from the IRQ thread. >> >> Is there any way we can do this automatically? Perhaps detecting that >> we're on a RT kernel or maybe that the user is running with RT priority? >> I find that module options are mostly misunderstood and misused. > > Alex, thanks for review. > > It's not easy to detect if the user is running with RT priority, since > sometimes the user start the thread and then set the scheduler priority > late. > > Also should we do this only for in kernel irqchip scenario and not for user > space handler, since in kernel irqchip has lower overhead? The overhead of the non-threaded IRQ handler is the same for kernel or userspace irqchip, since the handler just writes 1 to the eventfd. On RT kernels however can you call eventfd_signal from interrupt context? You cannot call spin_lock_irqsave (which can sleep) from a non-threaded interrupt handler, can you? You would need a raw spin lock. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
