With the implementation of napi-tx in virtio driver, we clean tx descriptors from rx napi handler, for the purpose of reducing tx complete interrupts. But this introduces a race where tx complete interrupt has been raised, but the handler finds there is no work to do because we have done the work in the previous rx interrupt handler. A similar issue exists with polling from start_xmit, it is however less common because of the delayed cb optimization of the split ring - but will likely affect the packed ring once that is more common. In particular, this was reported to lead to the following warning msg: [ 3588.010778] irq 38: nobody cared (try booting with the "irqpoll" option) [ 3588.017938] CPU: 4 PID: 0 Comm: swapper/4 Not tainted 5.3.0-19-generic #20~18.04.2-Ubuntu [ 3588.017940] Call Trace: [ 3588.017942] <IRQ> [ 3588.017951] dump_stack+0x63/0x85 [ 3588.017953] __report_bad_irq+0x35/0xc0 [ 3588.017955] note_interrupt+0x24b/0x2a0 [ 3588.017956] handle_irq_event_percpu+0x54/0x80 [ 3588.017957] handle_irq_event+0x3b/0x60 [ 3588.017958] handle_edge_irq+0x83/0x1a0 [ 3588.017961] handle_irq+0x20/0x30 [ 3588.017964] do_IRQ+0x50/0xe0 [ 3588.017966] common_interrupt+0xf/0xf [ 3588.017966] </IRQ> [ 3588.017989] handlers: [ 3588.020374] [<000000001b9f1da8>] vring_interrupt [ 3588.025099] Disabling IRQ #38 This patchset attempts to fix this by cleaning up a bunch of races related to the handling of sq callbacks (aka tx interrupts). Somewhat tested but I couldn't reproduce the original issues reported, sending out for help with testing. Wei, does this address the spurious interrupt issue you are observing? Could you confirm please? Thanks! changes from v2: Fixed a race condition in start_xmit: enable_cb_delayed was done as an optimization (to push out event index for split ring) so we did not have to care about it returning false (recheck). Now that we actually disable the cb we have to do test the return value and do the actual recheck. Michael S. Tsirkin (4): virtio_net: move tx vq operation under tx queue lock virtio_net: move txq wakeups under tx q lock virtio: fix up virtio_disable_cb virtio_net: disable cb aggressively drivers/net/virtio_net.c | 49 ++++++++++++++++++++++++++++-------- drivers/virtio/virtio_ring.c | 26 ++++++++++++++++++- 2 files changed, 64 insertions(+), 11 deletions(-) -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
