Osmo io » History » Revision 7
Revision 6 (laforge, 03/14/2024 07:51 AM) → Revision 7/8 (laforge, 03/14/2024 08:05 AM)
h1. osmo_io @osmo_io@ is the new (2023) way of ho we do I/O in osmocom projects. It moves from a raw select/poll abstraction (where every application performs its own read/write once the fd becomes readble/writable) to a submission/completion model, where the actual I/O is performed by the library, an the application just submits write requests (as @struct msgb@) and receives write-completion and read-completion call-backs. Apart from having more code reuse and a cleaner split between application and I/O library, this has the added advantage that the underlying operating system I/O mechanism can be swapped out without touching each and every application. Specifically, we have currently the following two back-ends implemented in libosmocore: * *POLL*: classic osmo_fd based implementation using @poll(2)@ (default) * *IO_URING*: a backend using the Linux kernel @io_uring(7)@ API The choice of back-end is done via setting the @LIBOSMO_IO_BACKEND@ environment variable. If you set it to IO_URING when starting an osmocom program, all sub-systems / interfaces ported over to the osmo_io API will make use of the @io_uring(7)@ API (via liburing). The main advantage of io_uring is performance. Benchmarking has shown that a classic, poll-based production osmo-bsc loaded with 400 TRX is spending about 40% of its CPU cycles in the system call overhad (sock_poll, tcp_poll and do_sys_poll) and a lot of system call entry/exit in general, due to the many small read/write/recvmsg/sendmsg/recfrom/sendto and poll calls. For more information, see: * the original discussion in #5751 * FIXME API reference at https://ftp.osmocom.org/api/latest/libosmocore/core/html/osmo__io_8c.html#details h2. Implementation status The below tables indicate the implementation status of the osmo_io migration: h3. Libraries |_.library/interface|_.protocol|_.transport|_.users|_.commit|_.issue| |libosmocore|gsmtap|UDP|everyone|"libosmocore":https://gerrit.osmocom.org/c/libosmocore/+/34743|#6213| |libosmo-mgcp-client|MGCP|UDP|osmo-bsc, osmo-msc, osmo-hnbgw|"osmo-mgw":https://gitea.osmocom.org/cellular-infrastructure/osmo-mgw/commit/8b524c9151177d681b35332146d7628fafd82846|#5754| |libosmogb ns2|NS|UDP|osmo-pcu, osmo-gbproxy, osmo-sgsn|"libosmocore":https://gitea.osmocom.org/osmocom/libosmocore/commit/eb9edbab54463cb705ec7b770e022a215ce503c7|#5751| |libosmo-netif|stream_cli|TCP|libosmo-sigtran(ipa), osmo-bsc(cbsp), osmo-cbc(cbsp)|"libosmo-netif":https://gitea.osmocom.org/osmocom/libosmo-netif/commit/0e7028f742dedefd9fccc2d5b26875fca4036f58|#5753| |libosmo-netif|stream_cli|SCTP|libosmo-sigtran|"libosmo-netif":https://gitea.osmocom.org/osmocom/libosmo-netif/commit/7e6d2e0f99ff095f4714f03b1ed991d6c9cb9c61|#5753| |libosmo-sigtran|xUA ASP (SUA, M3UA)|SCTP|osmo-bsc, osmo-msc, osmo-sgsn, osmo-hnbgw, osmo-smlc|"libosmo-sigtran":https://gitea.osmocom.org/osmocom/libosmo-sccp/commit/9257cd896e255403822bee6f87f5487a92fd3c11|#5752| h3. Program |_.program|_.Interface/protocol|_.transport|_.commit|_.issue| |osmo-gbproxy|Gb/NS|UDP|indirect via "libosmogb ns2":https://gitea.osmocom.org/osmocom/libosmocore/commit/eb9edbab54463cb705ec7b770e022a215ce503c7| |osmo-bsc|CBSP|TCP client+server|"osmo-bsc":https://gitea.osmocom.org/cellular-infrastructure/osmo-bsc/commit/85687bf176e4b9663f2396a27c28b49221c72fa3|#6170| |osmo-bsc|meas_feed|UDP|"osmo-bsc":https://gitea.osmocom.org/cellular-infrastructure/osmo-bsc/commit/ea388e1db1465afdcfd2796336732d29d80a2b9f| |osmo-bsc|MGCP|UDP|indirect via libosmo-mgcp-client|#5755| |osmo-bsc|M3UA/SUA/IPA|SCTP/TCP|indirect via libosmo-sigtran|#5755| |osmo-hnbgw|MGCP|UDP|indirect via libosmo-mgcp-client| |osmo-hnbgw|M3UA/SUA/IPA|SCTP/TCP|indirect via libosmo-sigtran| |osmo-msc|MGCP|UDP|indirect via libosmo-mgcp-client| |osmo-msc|M3UA/SUA/IPA|SCTP/TCP|indirect via libosmo-sigtran| |osmo-sgsn|M3UA/SUA/IPA|SCTP/TCP|indirect via libosmo-sigtran| |osmo-sgsn|Gb/NS|UDP|indirect via "libosmogb ns2":https://gitea.osmocom.org/osmocom/libosmocore/commit/eb9edbab54463cb705ec7b770e022a215ce503c7| |osmo-smlc|M3UA/SUA/IPA|SCTP/TCP|indirect via libosmo-sigtran| |osmo-stp|M3UA/SUA/IPA|SCTP/TCP|indirect via libosmo-sigtran|#5752| h2. Further reading * "wikipedia page on io_uring":https://en.wikipedia.org/wiki/Io_uring * "Efficient IO with io_uring":https://kernel.dk/io_uring.pdf by the io_uring creator Jens Axboe. * "io_uring and networking in 2023":https://kernel.dk/io_uring%20and%20networking%20in%202023.pdf
