| Message ID | 20250123231236.2657321-1-skhawaja@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Add support to do threaded napi busy poll | expand |
On Thu, 23 Jan 2025 23:12:32 +0000 Samiullah Khawaja wrote: > Extend the already existing support of threaded napi poll to do continuous > busy polling. ## Form letter - net-next-closed The merge window for v6.14 has begun and we have already posted our pull request. Therefore net-next is closed for new drivers, features, code refactoring and optimizations. We are currently accepting bug fixes only. Please repost when net-next reopens after Feb 3rd. RFC patches sent for review only are obviously welcome at any time. See: https://www.kernel.org/doc/html/next/process/maintainer-netdev.html#development-cycle
On Thu, Jan 23, 2025 at 11:12:32PM +0000, Samiullah Khawaja wrote: > Extend the already existing support of threaded napi poll to do continuous > busy polling. > > This is used for doing continuous polling of napi to fetch descriptors from > backing RX/TX queues for low latency applications. Allow enabling of threaded > busypoll using netlink so this can be enabled on a set of dedicated napis for > low latency applications. > > It allows enabling NAPI busy poll for any userspace application > indepdendent of userspace API being used for packet and event processing > (epoll, io_uring, raw socket APIs). Once enabled user can fetch the PID > of the kthread doing NAPI polling and set affinity, priority and > scheduler for it depending on the low-latency requirements. When you resubmit this after the merge window (or if you resubmit it as an RFC), would you mind CCing both me (jdamato@fastly.com) and Martin (mkarsten@uwaterloo.ca) ? We almost missed this revision after commenting on the previous version, since we weren't included in the CC list. Both Martin and I read through the cover letter and proposed changes and have several questions/comments, but given that the thread is marked as deferred/closed due to the merge window, we'll hold off on digging in until the next revision is posted.
Extend the already existing support of threaded napi poll to do continuous busy polling. This is used for doing continuous polling of napi to fetch descriptors from backing RX/TX queues for low latency applications. Allow enabling of threaded busypoll using netlink so this can be enabled on a set of dedicated napis for low latency applications. It allows enabling NAPI busy poll for any userspace application indepdendent of userspace API being used for packet and event processing (epoll, io_uring, raw socket APIs). Once enabled user can fetch the PID of the kthread doing NAPI polling and set affinity, priority and scheduler for it depending on the low-latency requirements. Currently threaded napi is only enabled at device level using sysfs. Add support to enable/disable threaded mode for a napi individually. This can be done using the netlink interface. Extend `napi-set` op in netlink spec that allows setting the `threaded` attribute of a napi. Extend the threaded attribute in napi struct to add an option to enable continuous busy polling. Extend the netlink and sysfs interface to allow enabled/disabling threaded busypolling at device or individual napi level. We use this for our AF_XDP based hard low-latency usecase using onload stack (https://github.com/Xilinx-CNS/onload) that runs in userspace. Our usecase is a fixed frequency RPC style traffic with fixed request/response size. We simulated this using neper by only starting next transaction when last one has completed. The experiment results are listed below, Setup: - Running on Google C3 VMs with idpf driver with following configurations. - IRQ affinity and coalascing is common for both experiments. - There is only 1 RX/TX queue configured. - First experiment enables busy poll using sysctl for both epoll and socket APIs. - Second experiment enables NAPI threaded busy poll for the full device using sysctl. Non threaded NAPI busy poll enabled using sysctl. ``` echo 400 | sudo tee /proc/sys/net/core/busy_poll echo 400 | sudo tee /proc/sys/net/core/busy_read echo 2 | sudo tee /sys/class/net/eth0/napi_defer_hard_irqs echo 15000 | sudo tee /sys/class/net/eth0/gro_flush_timeout ``` Results using following command, ``` sudo EF_NO_FAIL=0 EF_POLL_USEC=100000 taskset -c 3-10 onload -v \ --profile=latency ./neper/tcp_rr -Q 200 -R 400 -T 1 -F 50 \ -p 50,90,99,999 -H <IP> -l 10 ... ... num_transactions=2835 latency_min=0.000018976 latency_max=0.049642100 latency_mean=0.003243618 latency_stddev=0.010636847 latency_p50=0.000025270 latency_p90=0.005406710 latency_p99=0.049807350 latency_p99.9=0.049807350 ``` Results with napi threaded busy poll using following command, ``` sudo EF_NO_FAIL=0 EF_POLL_USEC=100000 taskset -c 3-10 onload -v \ --profile=latency ./neper/tcp_rr -Q 200 -R 400 -T 1 -F 50 \ -p 50,90,99,999 -H <IP> -l 10 ... ... num_transactions=460163 latency_min=0.000015707 latency_max=0.200182942 latency_mean=0.000019453 latency_stddev=0.000720727 latency_p50=0.000016950 latency_p90=0.000017270 latency_p99=0.000018710 latency_p99.9=0.000020150 ``` Here with NAPI threaded busy poll in a separate core, we are able to consistently poll the NAPI to keep latency to absolute minimum. And also we are able to do this without any major changes to the onload stack and threading model. v2: - Add documentation in napi.rst. - Provide experiment data and usecase details. - Update busy_poller selftest to include napi threaded poll testcase. - Define threaded mode enum in netlink interface. - Included NAPI threaded state in napi config to save/restore. Samiullah Khawaja (4): Add support to set napi threaded for individual napi net: Create separate gro_flush helper function Extend napi threaded polling to allow kthread based busy polling selftests: Add napi threaded busy poll test in `busy_poller` Documentation/ABI/testing/sysfs-class-net | 3 +- Documentation/netlink/specs/netdev.yaml | 14 ++ Documentation/networking/napi.rst | 80 ++++++++++- .../net/ethernet/atheros/atl1c/atl1c_main.c | 2 +- include/linux/netdevice.h | 24 +++- include/uapi/linux/netdev.h | 7 + net/core/dev.c | 127 ++++++++++++++---- net/core/net-sysfs.c | 2 +- net/core/netdev-genl-gen.c | 5 +- net/core/netdev-genl.c | 9 ++ tools/include/uapi/linux/netdev.h | 7 + tools/testing/selftests/net/busy_poll_test.sh | 25 +++- tools/testing/selftests/net/busy_poller.c | 14 +- 13 files changed, 282 insertions(+), 37 deletions(-)