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| author | Andrea Parri <parri.andrea@gmail.com> | 2024-01-31 17:49:34 +0300 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-02-15 19:04:12 +0300 |
| commit | a14d11a0f5f4105e0df96811dfa81dc5f79fecba (patch) | |
| tree | 5b581014e1cbf4e437de5afb74e8a9bff9b9e8eb /Documentation/scheduler | |
| parent | d6cfd1770f20392d7009ae1fdb04733794514fa9 (diff) | |
| download | linux-a14d11a0f5f4105e0df96811dfa81dc5f79fecba.tar.xz | |
membarrier: Create Documentation/scheduler/membarrier.rst
To gather the architecture requirements of the "private/global
expedited" membarrier commands. The file will be expanded to
integrate further information about the membarrier syscall (as
needed/desired in the future). While at it, amend some related
inline comments in the membarrier codebase.
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/r/20240131144936.29190-3-parri.andrea@gmail.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'Documentation/scheduler')
| -rw-r--r-- | Documentation/scheduler/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/scheduler/membarrier.rst | 39 |
2 files changed, 40 insertions, 0 deletions
diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst index 3170747226f6..43bd8a145b7a 100644 --- a/Documentation/scheduler/index.rst +++ b/Documentation/scheduler/index.rst @@ -7,6 +7,7 @@ Scheduler completion + membarrier sched-arch sched-bwc sched-deadline diff --git a/Documentation/scheduler/membarrier.rst b/Documentation/scheduler/membarrier.rst new file mode 100644 index 000000000000..2387804b1c63 --- /dev/null +++ b/Documentation/scheduler/membarrier.rst @@ -0,0 +1,39 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================== +membarrier() System Call +======================== + +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements +===================================================================== + +Memory barriers before updating rq->curr +---------------------------------------- + +The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDITED +require each architecture to have a full memory barrier after coming from +user-space, before updating rq->curr. This barrier is implied by the sequence +rq_lock(); smp_mb__after_spinlock() in __schedule(). The barrier matches a full +barrier in the proximity of the membarrier system call exit, cf. +membarrier_{private,global}_expedited(). + +Memory barriers after updating rq->curr +--------------------------------------- + +The commands MEMBARRIER_CMD_PRIVATE_EXPEDITED and MEMBARRIER_CMD_GLOBAL_EXPEDITED +require each architecture to have a full memory barrier after updating rq->curr, +before returning to user-space. The schemes providing this barrier on the various +architectures are as follows. + + - alpha, arc, arm, hexagon, mips rely on the full barrier implied by + spin_unlock() in finish_lock_switch(). + + - arm64 relies on the full barrier implied by switch_to(). + + - powerpc, riscv, s390, sparc, x86 rely on the full barrier implied by + switch_mm(), if mm is not NULL; they rely on the full barrier implied + by mmdrop(), otherwise. On powerpc and riscv, switch_mm() relies on + membarrier_arch_switch_mm(). + +The barrier matches a full barrier in the proximity of the membarrier system call +entry, cf. membarrier_{private,global}_expedited(). |