[RFC PATCH v2] Documentation/rv: Explain epoll and aborted sleeps
Chao Liu <[email protected]>
| Newsgroups | org.kernel.vger.linux-doc,org.kernel.vger.linux-kernel,org.kernel.vger.linux-trace-kernel |
|---|---|
| Message-ID | <[email protected]> |
epoll_wait() is a valid sleeping reason for real-time tasks because it uses PI-aware locking, but the rtapp sleep monitor documentation only discusses clock_nanosleep() and futexes. Document it. ABORT_SLEEP represents a task restoring TASK_RUNNING before entering the scheduler. Since the task does not actually block, it becomes runnable again without a wakeup sequence unsafe for real-time. Document this behavior. This RFC is based on Nam Cao's pending "rv: rtapp monitor update" v2 series: https://lore.kernel.org/r/[email protected] Signed-off-by: Chao Liu <[email protected]> --- Changes in v2: - Explain why epoll_wait() is RT-safe in terms of PI-aware locking. - Explain that ABORT_SLEEP does not require an RT-unsafe wakeup sequence. - Update the commit message accordingly. Link to v1: https://lore.kernel.org/linux-trace-kernel/[email protected]/ Documentation/trace/rv/monitor_rtapp.rst | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Documentation/trace/rv/monitor_rtapp.rst b/Documentation/trace/rv/monitor_rtapp.rst index 238b59395ff5..b95994ade14a 100644 --- a/Documentation/trace/rv/monitor_rtapp.rst +++ b/Documentation/trace/rv/monitor_rtapp.rst @@ -67,6 +67,8 @@ thread to sleep for one of the following reasons: variables as safe for real-time. As an alternative, the librtpi library exists to provide a conditional variable implementation that is correct for real-time applications in Linux. + - Real-time thread waiting for events using `epoll_wait`, which is a + real-time-safe syscall for sleeping as it uses PI-aware locking. Beside the reason for sleeping, the eventual waker should also be real-time-safe. Namely, one of: @@ -114,6 +116,10 @@ The monitor's specification is:: ALLOWLIST = BLOCK_ON_RT_MUTEX or FUTEX_LOCK_PI +`ABORT_SLEEP` represents a task restoring its state to `TASK_RUNNING` before +entering the scheduler. In this case, the task does not actually block, so the +task is back to runnable without any wakeup sequence unsafe for real-time. + Beside the scenarios described above, this specification also defines an allow list to handle some special cases: base-commit: 248951ddc14de84de3910f9b13f51491a8cd91df prerequisite-patch-id: d8b6c952a954662852e6b0684e0a3386eaab7f41 prerequisite-patch-id: 940f7637aeabe4ba15a09c048c6f48138406f332 prerequisite-patch-id: b99812692691f76d825778e01a2e771e058febd6 prerequisite-patch-id: 512c300dce2cb74ac9cc007f9234aa507ef5c008 -- 2.54.0