From 6f8b12d661d09b488b9ac879b8eafbd2cc4a1450 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 22 Apr 2020 09:13:27 -0700 Subject: net: napi: add hard irqs deferral feature Back in commit 3b47d30396ba ("net: gro: add a per device gro flush timer") we added the ability to arm one high resolution timer, that we used to keep not-complete packets in GRO engine a bit longer, hoping that further frames might be added to them. Since then, we added the napi_complete_done() interface, and commit 364b6055738b ("net: busy-poll: return busypolling status to drivers") allowed drivers to avoid re-arming NIC interrupts if we made a promise that their NAPI poll() handler would be called in the near future. This infrastructure can be leveraged, thanks to a new device parameter, which allows to arm the napi hrtimer, instead of re-arming the device hard IRQ. We have noticed that on some servers with 32 RX queues or more, the chit-chat between the NIC and the host caused by IRQ delivery and re-arming could hurt throughput by ~20% on 100Gbit NIC. In contrast, hrtimers are using local (percpu) resources and might have lower cost. The new tunable, named napi_defer_hard_irqs, is placed in the same hierarchy than gro_flush_timeout (/sys/class/net/ethX/) By default, both gro_flush_timeout and napi_defer_hard_irqs are zero. This patch does not change the prior behavior of gro_flush_timeout if used alone : NIC hard irqs should be rearmed as before. One concrete usage can be : echo 20000 >/sys/class/net/eth1/gro_flush_timeout echo 10 >/sys/class/net/eth1/napi_defer_hard_irqs If at least one packet is retired, then we will reset napi counter to 10 (napi_defer_hard_irqs), ensuring at least 10 periodic scans of the queue. On busy queues, this should avoid NIC hard IRQ, while before this patch IRQ avoidance was only possible if napi->poll() was exhausting its budget and not call napi_complete_done(). This feature also can be used to work around some non-optimal NIC irq coalescing strategies. Having the ability to insert XX usec delays between each napi->poll() can increase cache efficiency, since we increase batch sizes. It also keeps serving cpus not idle too long, reducing tail latencies. Co-developed-by: Luigi Rizzo Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/linux/netdevice.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 0750b54b3765..5a8d40f1ffe2 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -329,6 +329,7 @@ struct napi_struct { unsigned long state; int weight; + int defer_hard_irqs_count; unsigned long gro_bitmask; int (*poll)(struct napi_struct *, int); #ifdef CONFIG_NETPOLL @@ -1995,6 +1996,7 @@ struct net_device { struct bpf_prog __rcu *xdp_prog; unsigned long gro_flush_timeout; + int napi_defer_hard_irqs; rx_handler_func_t __rcu *rx_handler; void __rcu *rx_handler_data; -- cgit v1.2.3