Alexander Wetzel <alexander@xxxxxxxxxxxxxx> writes: > On 10.05.22 18:10, Felix Fietkau wrote: >> On 10.05.22 17:58, Alexander Wetzel wrote: >>> Let iTXQ drivers also register four queues in netdev and move queue >>> assignment to ndo_select_queue(), like it's done for other drivers. >>> >>> This gets rid of a special case in mac80211 and also increases the >>> chance that when we call skb_get_hash() the skb is still hot in the CPU >>> buffers. >>> >>> Signed-off-by: Alexander Wetzel <alexander@xxxxxxxxxxxxxx> >> >> This has the disadvantage of requiring a redundant sta lookup in the tx >> path for iTXQ drivers. I think the CPU cost of that one is probably >> higher than any potential gain from calling skb_get_hash a bit earlier. > > Found that one, yes. But why do we then not drop ndo_select_queue() for > all drivers? > > Or maybe just call skb_get_hash() in ndo_select_queue()... But I guess > then it would make more sense to move the ndo_select_queue() into > netdev, so all drivers get the optimization. The reason it's an optimisation for mac80211 is that we know skb_get_hash() will always be called later (when enqueueing into the TXQ). This is not always the case for other drivers, so that is probably a dubious optimisation to have in general. -Toke
