On Sun, Apr 27, 2014 at 06:03:04PM +0300, Michael S. Tsirkin wrote: > On Sun, Apr 27, 2014 at 10:35:41PM +0800, Amos Kong wrote: > > On Sat, Apr 19, 2014 at 12:08:15PM +0800, Amos Kong wrote: > > > > > > Hi all, > > > > > > I'm working on this item in Upstream Networking todolist: > > > > > > | - Sharing config interrupts > > > | Support more devices by sharing a single msi vector > > > | between multiple virtio devices. > > > | (Applies to virtio-blk too). > > > > > > I have this solution here, and only have draft patches of Solution > > > 1 & 2, let's discuss if solution 3 is feasible. > > > > > > * We should not introduce perf regression in this change > > > * little effect is acceptable because we are _sharing_ interrupt > > > > > > Solution 1: > > > ========== > > > share one LSI interrupt for configuration change of all virtio devices. > > > Draft patch: share_lsi_for_all_config.patch > > > > > > Solution 2: > > > ========== > > > share one MSI interrupt for configuration change of all virtio devices. > > > Draft patch: share_msix_for_all_config.patch > > > > > > Solution 3: > > > ========== > > > dynamic adjust interrupt policy when device is added or removed > > > Current: > > > ------- > > > - try to allocate a MSI to device's config > > > - try to allocate a MSI for each vq > > > - share one MSI for all vqs of one device > > > - share one LSI for config & vqs of one device > > > > > > additional dynamic policies: > > > --------------------------- > > > - if there is no enough MSI, adjust interrupt allocation for returning > > > some MSI > > > - try to find a device that allocated one MSI for each vq, change > > > it to share one MSI for saving the MSI > > > - try to share one MSI for config of all virtio_pci devices > > > - try to share one LSI for config of all devices > > > > > > - if device is removed, try to re-allocate freed MSI to existed > > > devices, if they aren't in best status (one MSI for config, one > > > MSI for each vq) > > > - if config of all devices is sharing one LSI, try to upgrade it to MSI > > > - if config of all devices is sharing one MSI, try to allocate one > > > MSI for configuration change of each device > > > - try to find a device that is sharing one MSI for all vqs, try to > > > allocate one MSI for each vq > > > > Hi Michael, Alex > > > > Any thoughts about this ? :) > > > > > > Thanks, Amos > > > I don't think we need to worry about dynamic. Dynamic policy can always get good balance. If we use a fixed policy, devices might share IRQ with some unused msix, or sometimes it's not fair enough for all devices. > Questions: just by using IRQF_SHARED, do we always end > up with a shared interrupt? Or only if system is running > out of vectors? In solution1: always share one LSI for config of all virtio devices In solution2: always share one MSI for config of all virtio devices > Did you test that interrupt is actually shared and all > handlers are called? Yes. I can find many devices (virtio.0, virtio.1,...) share same interrupt in guest's /proc/interrupts. And nics work well. > We don't stop after the 1st handler that > returned OK? When we set IRQF_SHARED flag, dev_id is necessary. In irq_wake_thread() it's used to identify the device for which the irq_thread should be woke. So when we share one IRQ, one single interrupt will only wake one handler once. -- Amos. -- 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
