> From: KY Srinivasan > Sent: Friday, July 17, 2015 23:33 > > From: Dexuan Cui > > Sent: Friday, July 17, 2015 3:01 AM > > > From: K. Y. Srinivasan > > > Sent: Friday, July 17, 2015 3:17 > > > Subject: [PATCH net-next 1/1] hv_netvsc: Wait for sub-channels to be > > processed > > > during probe > > > diff --git a/drivers/net/hyperv/hyperv_net.h > > b/drivers/net/hyperv/hyperv_net.h > > > ... > > > @@ -1116,6 +1127,9 @@ int rndis_filter_device_add(struct hv_device > > *dev, > > > num_possible_rss_qs = cpumask_weight(node_cpu_mask); > > > net_device->num_chn = min(num_possible_rss_qs, num_rss_qs); > > > > > > +num_rss_qs = net_device->num_chn - 1; > > > +net_device->num_sc_offered = num_rss_qs; > > > + > > > if (net_device->num_chn == 1) > > > goto out; > > > > > > @@ -1157,11 +1171,22 @@ int rndis_filter_device_add(struct hv_device > > *dev, > > > > > > ret = rndis_filter_set_rss_param(rndis_device, net_device- > > >num_chn); > > > > > > +/* > > > + * Wait for the host to send us the sub-channel offers. > > > + */ > > > +spin_lock_irqsave(&net_device->sc_lock, flags); > > > +sc_delta = net_device->num_chn - 1 - num_rss_qs; > > > +net_device->num_sc_offered -= sc_delta; > > > > Hi KY, > > IMO here the "-= " should be "+="? > > > > I think sc_delta is usually <= 0, meaning the host may allocate less > > subchannels than > > we expect. > > With "-=", net_device->num_sc_offered can become bigger -- this doesn't > > seem correct. > We control how many sub-channels we want the host to offer (say > sc_requested). Based on this > number we begin to track how many have actually been processed - we > decrement sc_requested > each time a sub-channel offer is processed. If the host were to actually offer all > that we have requested, > then checking for sc_requested to be zero is sufficient to ensure that we have > processed all the > potentially in-flight sub-channels. However, the host may choose to offer less > than what we had asked for > and the variable "delta" is tracking this difference. Since we are counting down > from what we had asked for > we have to subtract "delta" for proper accounting. Yes, I understand the rationale. Let me show the issue by example: Let's assume sc_requested is 7 and the host actually only offers 3 sub-channels: 1. Just before sending the NVSP_MSG5_TYPE_SUBCHANNEL message, we have net_device->num_chn == 8, num_rss_qs == 7 net_device->num_sc_offered == 7 2. Just after we get the reply of the message, net_device->num_chn == 4 sc_delta = net_device->num_chn - 1 - num_rss_qs, so sc_delta == 4 - 1 - 7 = -4 net_device->num_sc_offered -= sc_delta, so net_device->num_sc_offered == 7 - (-4) = 11. It's not zero, so we sleep on the wait_for_completion(). 3. Now we process the 3 sub-channel and net_device->num_sc_offered will become 11 -1 -1 -1 == 8 and no complete() will be invoked! That's why I think the "-=" in the line net_device->num_sc_offered -= sc_delta should be "+=". > > Why not use > > "net_device->num_sc_offered = net_device->num_chn - 1;" directly? > > At this point, net_device->num_chn has been the number of the actual > > channels. > > I am not sure what the question here is. num_sc_offered is initialized to the > number we > are going to ask and this is the number that will be decremented each time a > sub-channel > is processed. Since the host may decide to offer us less than what we had asked > and some > sub-channels may have already been processed (num_sc_offerred decremented > accordingly) > by the time we discover that the host has offered us less than what we asked for, > we adjust > num_sc_offered accordingly. Sorry, I had a misunderstanding here. Please just ignore this question. Thanks, -- Dexuan _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
