>>> Maybe I was wrong, but according to Michael's comment it looks like he >>> want >>> check affinity_hint_set just for speculative tx polling on rx napi >>> instead >>> of disabling it at all. >>> >>> And I'm not convinced this is really needed, driver only provide affinity >>> hint instead of affinity, so it's not guaranteed that tx and rx interrupt >>> are in the same vcpus. >> >> You're right. I made the restriction broader than the request, to really >> err >> on the side of caution for the initial merge of napi tx. And enabling >> the optimization is always a win over keeping it off, even without irq >> affinity. >> >> The cycle cost is significant without affinity regardless of whether the >> optimization is used. > > > Yes, I noticed this in the past too. > >> Though this is not limited to napi-tx, it is more >> pronounced in that mode than without napi. >> >> 1x TCP_RR for affinity configuration {process, rx_irq, tx_irq}: >> >> upstream: >> >> 1,1,1: 28985 Mbps, 278 Gcyc >> 1,0,2: 30067 Mbps, 402 Gcyc >> >> napi tx: >> >> 1,1,1: 34492 Mbps, 269 Gcyc >> 1,0,2: 36527 Mbps, 537 Gcyc (!) >> 1,0,1: 36269 Mbps, 394 Gcyc >> 1,0,0: 34674 Mbps, 402 Gcyc >> >> This is a particularly strong example. It is also representative >> of most RR tests. It is less pronounced in other streaming tests. >> 10x TCP_RR, for instance: >> >> upstream: >> >> 1,1,1: 42267 Mbps, 301 Gcyc >> 1,0,2: 40663 Mbps, 445 Gcyc >> >> napi tx: >> >> 1,1,1: 42420 Mbps, 303 Gcyc >> 1,0,2: 42267 Mbps, 431 Gcyc >> >> These numbers were obtained with the virtqueue_enable_cb_delayed >> optimization after xmit_skb, btw. It turns out that moving that before >> increases 1x TCP_RR further to ~39 Gbps, at the cost of reducing >> 100x TCP_RR a bit. > > > I see, so I think we can leave the affinity hint optimization/check for > future investigation: > > - to avoid endless optimization (e.g we may want to share a single > vector/napi for tx/rx queue pairs in the future) for this series. > - tx napi is disabled by default which means we can do optimization on top. Okay. I'll drop the vi->affinity_hint_set from the patch set for now. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization