Christian Borntraeger wrote: > Am Mittwoch, 12. Dezember 2007 schrieb Dor Laor: > >> I think the change below handles the race. Otherwise please detail the >> use case. >> > [...] > >>> @@ -292,6 +292,9 @@ static int virtnet_open(struct net_devic >>> return -ENOMEM; >>> >>> napi_enable(&vi->napi); >>> + >>> + vi->rvq->vq_ops->enable(vi->rvq); >>> + vi->svq->vq_ops->enable(vi->svq); >>> >>> >> If you change it to: >> if (!vi->rvq->vq_ops->enable(vi->rvq)) >> vi->rvq->vq_ops->kick(vi->rvq); >> if (!vi->rvq->vq_ops->enable(vi->svq)) >> vi->rvq->vq_ops->kick(vi->svq); >> >> You solve the race of packets already waiting in the queue without >> triggering the irq. >> > > Hmm, I dont fully understand your point. I think this will work as long as > the host has not consumed all inbound buffers. It will also require that > the host sends an additional packet, no? If no additional packet comes the > host has no reason to send an interrupt just because it got a notify > hypercall. kick inside a guest also does not trigger the poll routine. > > It also wont work on the following scenario: > in virtnet open we will allocate buffers and send them to the host using the > kick callback. The host can now use _all_ buffers for incoming data while > interrupts are still disabled and the guest is not running.( Lets say the > host bridge has lots of multicast traffic and the guest gets not scheduled > for a while). When the guest now continues and enables the interrupts > nothing happens. Doing a kick does not help, as the host code will bail out > with "no dma memory for transfer". > > Christian > > You're right I got confused somehow. So in that case setting the driver status field on open in addition to your enable will do the trick. On DRIVER_OPEN the host will trigger an interrupt if the queue is not empty.. Thanks, Dor
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