This patch series implements a new char misc driver, /dev/ntsync, which is used to implement Windows NT synchronization primitives.
NT synchronization primitives are unique in that the wait functions both are vectored, operate on multiple types of object with different behaviour (mutex, semaphore, event), and affect the state of the objects they wait on. This model is not compatible with existing kernel synchronization objects or interfaces, and therefore the ntsync driver implements its own wait queues and locking.
This patch series is rebased against the "char-misc-next" branch of gregkh/char-misc.git.
== Background ==
The Wine project emulates the Windows API in user space. One particular part of that API, namely the NT synchronization primitives, have historically been implemented via RPC to a dedicated "kernel" process. However, more recent applications use these APIs more strenuously, and the overhead of RPC has become a bottleneck.
The NT synchronization APIs are too complex to implement on top of existing primitives without sacrificing correctness. Certain operations, such as NtPulseEvent() or the "wait-for-all" mode of NtWaitForMultipleObjects(), require direct control over the underlying wait queue, and implementing a wait queue sufficiently robust for Wine in user space is not possible. This proposed driver, therefore, implements the problematic interfaces directly in the Linux kernel.
This driver was presented at Linux Plumbers Conference 2023. For those further interested in the history of synchronization in Wine and past attempts to solve this problem in user space, a recording of the presentation can be viewed here:
https://www.youtube.com/watch?v=NjU4nyWyhU8
== Performance ==
The performance measurements described below are copied from earlier versions of the patch set. While some of the code has changed, I do not currently anticipate that it has changed drastically enough to affect those measurements.
The gain in performance varies wildly depending on the application in question and the user's hardware. For some games NT synchronization is not a bottleneck and no change can be observed, but for others frame rate improvements of 50 to 150 percent are not atypical. The following table lists frame rate measurements from a variety of games on a variety of hardware, taken by users Dmitry Skvortsov, FuzzyQuils, OnMars, and myself:
Game Upstream ntsync improvement =========================================================================== Anger Foot 69 99 43% Call of Juarez 99.8 224.1 125% Dirt 3 110.6 860.7 678% Forza Horizon 5 108 160 48% Lara Croft: Temple of Osiris 141 326 131% Metro 2033 164.4 199.2 21% Resident Evil 2 26 77 196% The Crew 26 51 96% Tiny Tina's Wonderlands 130 360 177% Total War Saga: Troy 109 146 34% ===========================================================================
== Patches ==
The intended semantics of the patches are broadly intended to match those of the corresponding Windows functions. For those not already familiar with the Windows functions (or their undocumented behaviour), patch 27/28 provides a detailed specification, and individual patches also include a brief description of the API they are implementing.
The patches making use of this driver in Wine can be retrieved or browsed here:
https://repo.or.cz/wine/zf.git/shortlog/refs/heads/ntsync7
== Previous versions ==
Changes from v6:
* rename NTSYNC_IOC_SEM_POST to NTSYNC_IOC_SEM_RELEASE (matching the NT terminology instead of POSIX),
* change object creation ioctls to return the fds directly in the return value instead of through the args struct, which simplifies the API a bit.
* Link to v6: https://lore.kernel.org/lkml/20241209185904.507350-1-zfigura@codeweavers.com... * Link to v5: https://lore.kernel.org/lkml/20240519202454.1192826-1-zfigura@codeweavers.co... * Link to v4: https://lore.kernel.org/lkml/20240416010837.333694-1-zfigura@codeweavers.com... * Link to v3: https://lore.kernel.org/lkml/20240329000621.148791-1-zfigura@codeweavers.com... * Link to v2: https://lore.kernel.org/lkml/20240219223833.95710-1-zfigura@codeweavers.com/ * Link to v1: https://lore.kernel.org/lkml/20240214233645.9273-1-zfigura@codeweavers.com/ * Link to RFC v2: https://lore.kernel.org/lkml/20240131021356.10322-1-zfigura@codeweavers.com/ * Link to RFC v1: https://lore.kernel.org/lkml/20240124004028.16826-1-zfigura@codeweavers.com/
Elizabeth Figura (30): ntsync: Return the fd from NTSYNC_IOC_CREATE_SEM. ntsync: Rename NTSYNC_IOC_SEM_POST to NTSYNC_IOC_SEM_RELEASE. ntsync: Introduce NTSYNC_IOC_WAIT_ANY. ntsync: Introduce NTSYNC_IOC_WAIT_ALL. ntsync: Introduce NTSYNC_IOC_CREATE_MUTEX. ntsync: Introduce NTSYNC_IOC_MUTEX_UNLOCK. ntsync: Introduce NTSYNC_IOC_MUTEX_KILL. ntsync: Introduce NTSYNC_IOC_CREATE_EVENT. ntsync: Introduce NTSYNC_IOC_EVENT_SET. ntsync: Introduce NTSYNC_IOC_EVENT_RESET. ntsync: Introduce NTSYNC_IOC_EVENT_PULSE. ntsync: Introduce NTSYNC_IOC_SEM_READ. ntsync: Introduce NTSYNC_IOC_MUTEX_READ. ntsync: Introduce NTSYNC_IOC_EVENT_READ. ntsync: Introduce alertable waits. selftests: ntsync: Add some tests for semaphore state. selftests: ntsync: Add some tests for mutex state. selftests: ntsync: Add some tests for NTSYNC_IOC_WAIT_ANY. selftests: ntsync: Add some tests for NTSYNC_IOC_WAIT_ALL. selftests: ntsync: Add some tests for wakeup signaling with WINESYNC_IOC_WAIT_ANY. selftests: ntsync: Add some tests for wakeup signaling with WINESYNC_IOC_WAIT_ALL. selftests: ntsync: Add some tests for manual-reset event state. selftests: ntsync: Add some tests for auto-reset event state. selftests: ntsync: Add some tests for wakeup signaling with events. selftests: ntsync: Add tests for alertable waits. selftests: ntsync: Add some tests for wakeup signaling via alerts. selftests: ntsync: Add a stress test for contended waits. maintainers: Add an entry for ntsync. docs: ntsync: Add documentation for the ntsync uAPI. ntsync: No longer depend on BROKEN.
Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/ntsync.rst | 385 +++++ MAINTAINERS | 9 + drivers/misc/Kconfig | 1 - drivers/misc/ntsync.c | 992 +++++++++++- include/uapi/linux/ntsync.h | 42 +- tools/testing/selftests/Makefile | 1 + .../selftests/drivers/ntsync/.gitignore | 1 + .../testing/selftests/drivers/ntsync/Makefile | 7 + tools/testing/selftests/drivers/ntsync/config | 1 + .../testing/selftests/drivers/ntsync/ntsync.c | 1343 +++++++++++++++++ 11 files changed, 2767 insertions(+), 16 deletions(-) create mode 100644 Documentation/userspace-api/ntsync.rst create mode 100644 tools/testing/selftests/drivers/ntsync/.gitignore create mode 100644 tools/testing/selftests/drivers/ntsync/Makefile create mode 100644 tools/testing/selftests/drivers/ntsync/config create mode 100644 tools/testing/selftests/drivers/ntsync/ntsync.c
base-commit: cdd30ebb1b9f36159d66f088b61aee264e649d7a