On 02.06.14 09:49, Eric Auger wrote:
This patch aims at optimizing IRQ handling using irqfd framework. It brings significant performance improvement over "traditional" IRQ handling introduced in : "vfio: Add initial IRQ support in platform device". This new IRQ handling method depends on kernel KVM irqfd/GSI routing capability. The IRQ handling method can be dynamically chosen (default is irqfd, if kernel supports it obviously). For example to disable irqfd handling, use: -device vfio-platform,vfio_device="fff51000.ethernet",\ compat="calxeda/hb-xgmac",mmap-timeout-ms=110,irqfd=false\ Performances are improved for the following reasons: - eventfds signalled by the VFIO platform driver are handled on kernel side by the KVM irqfd framework. - the end of interrupt(EOI) is trapped at GIC level and not at MMIO region level. As a reminder, in traditional IRQ handling QEMU assumed the first guest access to a device MMIO region after IRQ hit was the IRQ status register reset. This trap was approximate and obliged to swap to slow path after IRQ hit. A mmap timer mechanism enabled to swap back to fast path after the mmap period introducing extra complexity. Now GIC detects the completion of the virtual IRQ and signals a resampler eventfd on maintenance IRQ. The corresponding handler re-enables the physical IRQ.
Ah, so if you're using irqfd you do unmask the interrupt on EOI. Why not without irqfd? And if the answer is "because it's too difficult" - why support VFIO without irqfd at all then?
Alex _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
