| Message ID | 20201119083024.119566-1-bjorn.topel@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Introduce preferred busy-polling | expand |
On Thu, 19 Nov 2020 at 09:30, Björn Töpel <bjorn.topel@gmail.com> wrote: > > This series introduces three new features: > > 1. A new "heavy traffic" busy-polling variant that works in concert > with the existing napi_defer_hard_irqs and gro_flush_timeout knobs. > > 2. A new socket option that let a user change the busy-polling NAPI > budget. > > 3. Allow busy-polling to be performed on XDP sockets. > > The existing busy-polling mode, enabled by the SO_BUSY_POLL socket > option or system-wide using the /proc/sys/net/core/busy_read knob, is > an opportunistic. That means that if the NAPI context is not > scheduled, it will poll it. If, after busy-polling, the budget is > exceeded the busy-polling logic will schedule the NAPI onto the > regular softirq handling. > > One implication of the behavior above is that a busy/heavy loaded NAPI > context will never enter/allow for busy-polling. Some applications > prefer that most NAPI processing would be done by busy-polling. > > This series adds a new socket option, SO_PREFER_BUSY_POLL, that works > in concert with the napi_defer_hard_irqs and gro_flush_timeout > knobs. The napi_defer_hard_irqs and gro_flush_timeout knobs were > introduced in commit 6f8b12d661d0 ("net: napi: add hard irqs deferral > feature"), and allows for a user to defer interrupts to be enabled and > instead schedule the NAPI context from a watchdog timer. When a user > enables the SO_PREFER_BUSY_POLL, again with the other knobs enabled, > and the NAPI context is being processed by a softirq, the softirq NAPI > processing will exit early to allow the busy-polling to be performed. > > If the application stops performing busy-polling via a system call, > the watchdog timer defined by gro_flush_timeout will timeout, and > regular softirq handling will resume. > > In summary; Heavy traffic applications that prefer busy-polling over > softirq processing should use this option. > Eric/Jakub, any more thoughts/input? Tomatoes? :-P Thank you, Björn
On Mon, 23 Nov 2020 14:31:14 +0100 Björn Töpel wrote:
> Eric/Jakub, any more thoughts/input? Tomatoes? :-P
Looking now, sorry for the delay. Somehow patches without net in their
tag feel like they can wait..
On Thu, 19 Nov 2020 09:30:14 +0100 Björn Töpel wrote: > Performance netperf UDP_RR: > > Note that netperf UDP_RR is not a heavy traffic tests, and preferred > busy-polling is not typically something we want to use here. > > $ echo 20 | sudo tee /proc/sys/net/core/busy_read > $ netperf -H 192.168.1.1 -l 30 -t UDP_RR -v 2 -- \ > -o min_latency,mean_latency,max_latency,stddev_latency,transaction_rate > > busy-polling blocking sockets: 12,13.33,224,0.63,74731.177 > > I hacked netperf to use non-blocking sockets and re-ran: > > busy-polling non-blocking sockets: 12,13.46,218,0.72,73991.172 > prefer busy-polling non-blocking sockets: 12,13.62,221,0.59,73138.448 > > Using the preferred busy-polling mode does not impact performance. > > The above tests was done for the 'ice' driver. Any interest in this work form ADQ folks? I recall they were using memcache with busy polling for their tests, it'd cool to see how much this helps memcache on P99+ latency!
This series introduces three new features: 1. A new "heavy traffic" busy-polling variant that works in concert with the existing napi_defer_hard_irqs and gro_flush_timeout knobs. 2. A new socket option that let a user change the busy-polling NAPI budget. 3. Allow busy-polling to be performed on XDP sockets. The existing busy-polling mode, enabled by the SO_BUSY_POLL socket option or system-wide using the /proc/sys/net/core/busy_read knob, is an opportunistic. That means that if the NAPI context is not scheduled, it will poll it. If, after busy-polling, the budget is exceeded the busy-polling logic will schedule the NAPI onto the regular softirq handling. One implication of the behavior above is that a busy/heavy loaded NAPI context will never enter/allow for busy-polling. Some applications prefer that most NAPI processing would be done by busy-polling. This series adds a new socket option, SO_PREFER_BUSY_POLL, that works in concert with the napi_defer_hard_irqs and gro_flush_timeout knobs. The napi_defer_hard_irqs and gro_flush_timeout knobs were introduced in commit 6f8b12d661d0 ("net: napi: add hard irqs deferral feature"), and allows for a user to defer interrupts to be enabled and instead schedule the NAPI context from a watchdog timer. When a user enables the SO_PREFER_BUSY_POLL, again with the other knobs enabled, and the NAPI context is being processed by a softirq, the softirq NAPI processing will exit early to allow the busy-polling to be performed. If the application stops performing busy-polling via a system call, the watchdog timer defined by gro_flush_timeout will timeout, and regular softirq handling will resume. In summary; Heavy traffic applications that prefer busy-polling over softirq processing should use this option. Patch 6 touches a lot of drivers, so the Cc: list is grossly long. Example usage: $ echo 2 | sudo tee /sys/class/net/ens785f1/napi_defer_hard_irqs $ echo 200000 | sudo tee /sys/class/net/ens785f1/gro_flush_timeout Note that the timeout should be larger than the userspace processing window, otherwise the watchdog will timeout and fall back to regular softirq processing. Enable the SO_BUSY_POLL/SO_PREFER_BUSY_POLL options on your socket. Performance simple UDP ping-pong: A packet generator blasts UDP packets from a packet generator to a certain {src,dst}IP/port, so a dedicated ksoftirq will be busy handling the packets at a certain core. A simple UDP test program that simply does recvfrom/sendto is running at the host end. Throughput in pps and RTT latency is measured at the packet generator. /proc/sys/net/core/busy_read is set (20). Min Max Avg (usec) 1. Blocking 2-cores: 490Kpps 1218.192 1335.427 1271.083 2. Blocking, 1-core: 155Kpps 1327.195 17294.855 4761.367 3. Non-blocking, 2-cores: 475Kpps 1221.197 1330.465 1270.740 4. Non-blocking, 1-core: 3Kpps 29006.482 37260.465 33128.367 5. Non-blocking, prefer busy-poll, 1-core: 420Kpps 1202.535 5494.052 4885.443 Scenario 2 and 5 shows when the new option should be used. Throughput go from 155 to 420Kpps, average latency are similar, but the tail latencies are much better for the latter. Performance XDP sockets: Again, a packet generator blasts UDP packets from a packet generator to a certain {src,dst}IP/port. Today, running XDP sockets sample on the same core as the softirq handling, performance tanks mainly because we do not yield to user-space when the XDP socket Rx queue is full. # taskset -c 5 ./xdpsock -i ens785f1 -q 5 -n 1 -r Rx: 64Kpps # # biased busy-polling, budget 8 # taskset -c 5 ./xdpsock -i ens785f1 -q 5 -n 1 -r -B -b 8 Rx 9.9Mpps # # biased busy-polling, budget 64 # taskset -c 5 ./xdpsock -i ens785f1 -q 5 -n 1 -r -B -b 64 Rx: 19.3Mpps # # biased busy-polling, budget 256 # taskset -c 5 ./xdpsock -i ens785f1 -q 5 -n 1 -r -B -b 256 Rx: 21.4Mpps # # biased busy-polling, budget 512 # taskset -c 5 ./xdpsock -i ens785f1 -q 5 -n 1 -r -B -b 512 Rx: 21.7Mpps Compared to the two-core case: # taskset -c 4 ./xdpsock -i ens785f1 -q 20 -n 1 -r Rx: 20.7Mpps We're getting better single-core performance than two, for this naïve drop scenario. Performance netperf UDP_RR: Note that netperf UDP_RR is not a heavy traffic tests, and preferred busy-polling is not typically something we want to use here. $ echo 20 | sudo tee /proc/sys/net/core/busy_read $ netperf -H 192.168.1.1 -l 30 -t UDP_RR -v 2 -- \ -o min_latency,mean_latency,max_latency,stddev_latency,transaction_rate busy-polling blocking sockets: 12,13.33,224,0.63,74731.177 I hacked netperf to use non-blocking sockets and re-ran: busy-polling non-blocking sockets: 12,13.46,218,0.72,73991.172 prefer busy-polling non-blocking sockets: 12,13.62,221,0.59,73138.448 Using the preferred busy-polling mode does not impact performance. The above tests was done for the 'ice' driver. Thanks to Jakub for suggesting this busy-polling addition [1], and Eric for all input/review! Changes: rfc-v1 [2] -> rfc-v2: * Changed name from bias to prefer. * Base the work on Eric's/Luigi's defer irq/gro timeout work. * Proper GRO flushing. * Build issues for some XDP drivers. rfc-v2 [3] -> v1: * Fixed broken qlogic build. * Do not trigger an IPI (XDP socket wakeup) when busy-polling is enabled. v1 [4] -> v2: * Added napi_id to socionext driver, and added Ilias Acked-by:. (Ilias) * Added a samples patch to improve busy-polling for xdpsock/l2fwd. * Correctly mark atomic operations with {WRITE,READ}_ONCE, to make KCSAN and the code readers happy. (Eric) * Check NAPI budget not to exceed U16_MAX. (Eric) * Added kdoc. v2 [5] -> v3: * Collected Acked-by:. * Check NAPI disable prior prefer busy-polling. (Jakub) * Added napi_id registration for virtio-net. (Michael) * Added napi_id registration for veth. [1] https://lore.kernel.org/netdev/20200925120652.10b8d7c5@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com/ [2] https://lore.kernel.org/bpf/20201028133437.212503-1-bjorn.topel@gmail.com/ [3] https://lore.kernel.org/bpf/20201105102812.152836-1-bjorn.topel@gmail.com/ [4] https://lore.kernel.org/bpf/20201112114041.131998-1-bjorn.topel@gmail.com/ [5] https://lore.kernel.org/bpf/20201116110416.10719-1-bjorn.topel@gmail.com/ Björn Töpel (10): net: introduce preferred busy-polling net: add SO_BUSY_POLL_BUDGET socket option xsk: add support for recvmsg() xsk: check need wakeup flag in sendmsg() xsk: add busy-poll support for {recv,send}msg() xsk: propagate napi_id to XDP socket Rx path samples/bpf: use recvfrom() in xdpsock/rxdrop samples/bpf: use recvfrom() in xdpsock/l2fwd samples/bpf: add busy-poll support to xdpsock samples/bpf: add option to set the busy-poll budget arch/alpha/include/uapi/asm/socket.h | 3 + arch/mips/include/uapi/asm/socket.h | 3 + arch/parisc/include/uapi/asm/socket.h | 3 + arch/sparc/include/uapi/asm/socket.h | 3 + drivers/net/ethernet/amazon/ena/ena_netdev.c | 2 +- drivers/net/ethernet/broadcom/bnxt/bnxt.c | 2 +- .../ethernet/cavium/thunder/nicvf_queues.c | 2 +- .../net/ethernet/freescale/dpaa2/dpaa2-eth.c | 2 +- drivers/net/ethernet/intel/i40e/i40e_txrx.c | 2 +- drivers/net/ethernet/intel/ice/ice_base.c | 4 +- drivers/net/ethernet/intel/ice/ice_txrx.c | 2 +- drivers/net/ethernet/intel/igb/igb_main.c | 2 +- drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 2 +- .../net/ethernet/intel/ixgbevf/ixgbevf_main.c | 2 +- drivers/net/ethernet/marvell/mvneta.c | 2 +- .../net/ethernet/marvell/mvpp2/mvpp2_main.c | 4 +- drivers/net/ethernet/mellanox/mlx4/en_rx.c | 2 +- .../net/ethernet/mellanox/mlx5/core/en_main.c | 2 +- .../ethernet/netronome/nfp/nfp_net_common.c | 2 +- drivers/net/ethernet/qlogic/qede/qede_main.c | 2 +- drivers/net/ethernet/sfc/rx_common.c | 2 +- drivers/net/ethernet/socionext/netsec.c | 2 +- drivers/net/ethernet/ti/cpsw_priv.c | 2 +- drivers/net/hyperv/netvsc.c | 2 +- drivers/net/tun.c | 2 +- drivers/net/veth.c | 12 ++- drivers/net/virtio_net.c | 2 +- drivers/net/xen-netfront.c | 2 +- fs/eventpoll.c | 3 +- include/linux/netdevice.h | 35 +++++--- include/net/busy_poll.h | 27 ++++-- include/net/sock.h | 6 ++ include/net/xdp.h | 3 +- include/uapi/asm-generic/socket.h | 3 + net/core/dev.c | 89 ++++++++++++++----- net/core/sock.c | 19 ++++ net/core/xdp.c | 3 +- net/xdp/xsk.c | 53 ++++++++++- net/xdp/xsk_buff_pool.c | 13 ++- samples/bpf/xdpsock_user.c | 78 ++++++++++------ 40 files changed, 299 insertions(+), 107 deletions(-) base-commit: 4e99d115d865d45e17e83478d757b58d8fa66d3c