Re: [PATCH net] virtio-net: suppress bad irq warning for tx napi

On Wed, Feb 3, 2021 at 12:33 AM Jason Wang [off-list ref] wrote:

On 2021/2/2 下午10:37, Willem de Bruijn wrote:

quoted

On Mon, Feb 1, 2021 at 10:09 PM Jason Wang [off-list ref] wrote:

quoted

On 2021/1/29 上午8:21, Wei Wang wrote:

quoted

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 could introduce a race where tx complete
interrupt has been raised, but the handler found there is no work to do
because we have done the work in the previous rx interrupt handler.
This could 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 patch adds a new param to struct vring_virtqueue, and we set it for
tx virtqueues if napi-tx is enabled, to suppress the warning in such
case.

Fixes: 7b0411ef4aa6 ("virtio-net: clean tx descriptors from rx napi")
Reported-by: Rick Jones <redacted>
Signed-off-by: Wei Wang <redacted>
Signed-off-by: Willem de Bruijn <willemb@google.com>

Please use get_maintainer.pl to make sure Michael and me were cced.

Will do. Sorry about that. I suggested just the virtualization list, my bad.

quoted

quoted

---
   drivers/net/virtio_net.c     | 19 ++++++++++++++-----
   drivers/virtio/virtio_ring.c | 16 ++++++++++++++++
   include/linux/virtio.h       |  2 ++
   3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 508408fbe78f..e9a3f30864e8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -1303,13 +1303,22 @@ static void virtnet_napi_tx_enable(struct virtnet_info *vi,
               return;
       }

+     /* With napi_tx enabled, free_old_xmit_skbs() could be called from
+      * rx napi handler. Set work_steal to suppress bad irq warning for
+      * IRQ_NONE case from tx complete interrupt handler.
+      */
+     virtqueue_set_work_steal(vq, true);
+
       return virtnet_napi_enable(vq, napi);

Do we need to force the ordering between steal set and napi enable?

The warning only occurs after one hundred spurious interrupts, so not
really.

Ok, so it looks like a hint. Then I wonder how much value do we need to
introduce helper like virtqueue_set_work_steal() that allows the caller
to toggle. How about disable the check forever during virtqueue
initialization?

Yes, that is even simpler.

We still need the helper, as the internal variables of vring_virtqueue
are not accessible from virtio-net. An earlier patch added the
variable to virtqueue itself, but I think it belongs in
vring_virtqueue. And the helper is not a lot of code.
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization