On Thu, 2019-06-13 at 09:37 +0200, Magnus Karlsson wrote: > This patch set adds support for a new flag called need_wakeup in the > AF_XDP Tx and fill rings. When this flag is set by the driver, it > means that the application has to explicitly wake up the kernel Rx > (for the bit in the fill ring) or kernel Tx (for bit in the Tx ring) > processing by issuing a syscall. Poll() can wake up both and sendto() > will wake up Tx processing only. > > The main reason for introducing this new flag is to be able to > efficiently support the case when application and driver is executing > on the same core. Previously, the driver was just busy-spinning on > the > fill ring if it ran out of buffers in the HW and there were none to > get from the fill ring. This approach works when the application and > driver is running on different cores as the application can replenish > the fill ring while the driver is busy-spinning. Though, this is a > lousy approach if both of them are running on the same core as the > probability of the fill ring getting more entries when the driver is > busy-spinning is zero. With this new feature the driver now sets the > need_wakeup flag and returns to the application. The application can > then replenish the fill queue and then explicitly wake up the Rx > processing in the kernel using the syscall poll(). For Tx, the flag > is > only set to one if the driver has no outstanding Tx completion > interrupts. If it has some, the flag is zero as it will be woken up > by > a completion interrupt anyway. This flag can also be used in other > situations where the driver needs to be woken up explicitly. > > As a nice side effect, this new flag also improves the Tx performance > of the case where application and driver are running on two different > cores as it reduces the number of syscalls to the kernel. The kernel > tells user space if it needs to be woken up by a syscall, and this > eliminates many of the syscalls. The Rx performance of the 2-core > case > is on the other hand slightly worse, since there is a need to use a > syscall now to wake up the driver, instead of the driver > busy-spinning. It does waste less CPU cycles though, which might lead > to better overall system performance. > > This new flag needs some simple driver support. If the driver does > not > support it, the Rx flag is always zero and the Tx flag is always > one. This makes any application relying on this feature default to > the > old behavior of not requiring any syscalls in the Rx path and always > having to call sendto() in the Tx path. > > For backwards compatibility reasons, this feature has to be > explicitly > turned on using a new bind flag (XDP_USE_NEED_WAKEUP). I recommend > that you always turn it on as it has a large positive performance > impact for the one core case and does not degrade 2 core performance > and actually improves it for Tx heavy workloads. > > Here are some performance numbers measured on my local, > non-performance optimized development system. That is why you are > seeing numbers lower than the ones from Björn and Jesper. 64 byte > packets at 40Gbit/s line rate. All results in Mpps. Cores == 1 means > that both application and driver is executing on the same core. Cores > == 2 that they are on different cores. > > Applications > need_wakeup cores txpush rxdrop l2fwd > --------------------------------------------------------------- > n 1 0.07 0.06 0.03 > y 1 21.6 8.2 6.5 > n 2 32.3 11.7 8.7 > y 2 33.1 11.7 8.7 > > Overall, the need_wakeup flag provides the same or better performance > in all the micro-benchmarks. The reduction of sendto() calls in > txpush > is large. Only a few per second is needed. For l2fwd, the drop is 50% > for the 1 core case and more than 99.9% for the 2 core case. Do not > know why I am not seeing the same drop for the 1 core case yet. > > The name and inspiration of the flag has been taken from io_uring by > Jens Axboe. Details about this feature in io_uring can be found in > http://kernel.dk/io_uring.pdf, section 8.3. It also addresses most of > the denial of service and sendto() concerns raised by Maxim > Mikityanskiy in https://www.spinics.net/lists/netdev/msg554657.html. > > The typical Tx part of an application will have to change from: > > ret = sendto(fd,....) > > to: > > if (xsk_ring_prod__needs_wakeup(&xsk->tx)) > ret = sendto(fd,....) > > and th Rx part from: > > rcvd = xsk_ring_cons__peek(&xsk->rx, BATCH_SIZE, &idx_rx); > if (!rcvd) > return; > > to: > > rcvd = xsk_ring_cons__peek(&xsk->rx, BATCH_SIZE, &idx_rx); > if (!rcvd) { > if (xsk_ring_prod__needs_wakeup(&xsk->umem->fq)) > ret = poll(fd,.....); > return; > } > > This patch has been applied against commit aee450cbe482 ("bpf: > silence warning messages in core") > > Structure of the patch set: > > Patch 1: Replaces the ndo_xsk_async_xmit with ndo_xsk_wakeup to > support waking up both Rx and Tx processing > Patch 2: Implements the need_wakeup functionality in common code > Patch 3-4: Add need_wakeup support to the i40e and ixgbe drivers > Patch 5: Add need_wakeup support to libbpf > Patch 6: Add need_wakeup support to the xdpsock sample application > > Thanks: Magnus Since the i40e and ixgbe changes will not apply against my dev-queue branch (with the current queue of i40e and ixgbe changes), can you please rebase against my next-queue tree (dev-queue branch) when you submit v2? It will make it easier for me to apply and have validation verify the changes. > > Magnus Karlsson (6): > xsk: replace ndo_xsk_async_xmit with ndo_xsk_wakeup > xsk: add support for need_wakeup flag in AF_XDP rings > i40e: add support for AF_XDP need_wakup feature > ixgbe: add support for AF_XDP need_wakup feature > libbpf: add support for need_wakeup flag in AF_XDP part > samples/bpf: add use of need_sleep flag in xdpsock > > drivers/net/ethernet/intel/i40e/i40e_main.c | 5 +- > drivers/net/ethernet/intel/i40e/i40e_xsk.c | 23 ++- > drivers/net/ethernet/intel/i40e/i40e_xsk.h | 2 +- > drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 5 +- > .../net/ethernet/intel/ixgbe/ixgbe_txrx_common.h | 2 +- > drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 20 ++- > include/linux/netdevice.h | 18 +- > include/net/xdp_sock.h | 33 +++- > include/uapi/linux/if_xdp.h | 13 ++ > net/xdp/xdp_umem.c | 6 +- > net/xdp/xsk.c | 93 +++++++++- > net/xdp/xsk_queue.h | 1 + > samples/bpf/xdpsock_user.c | 191 > +++++++++++++-------- > tools/include/uapi/linux/if_xdp.h | 13 ++ > tools/lib/bpf/xsk.c | 4 + > tools/lib/bpf/xsk.h | 6 + > 16 files changed, 343 insertions(+), 92 deletions(-) > > -- > 2.7.4 > _______________________________________________ > Intel-wired-lan mailing list > Intel-wired-lan@xxxxxxxxxx > https://lists.osuosl.org/mailman/listinfo/intel-wired-lan
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