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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
commit | ace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch) | |
tree | b2d64bc10158fdd5497876388cd68142ca374ed3 /Documentation/arch/arm/swp_emulation.rst | |
parent | Initial commit. (diff) | |
download | linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip |
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/arch/arm/swp_emulation.rst')
-rw-r--r-- | Documentation/arch/arm/swp_emulation.rst | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/arch/arm/swp_emulation.rst b/Documentation/arch/arm/swp_emulation.rst new file mode 100644 index 0000000000..bf205e3de3 --- /dev/null +++ b/Documentation/arch/arm/swp_emulation.rst @@ -0,0 +1,27 @@ +Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE) +--------------------------------------------------------------------- + +ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommends +moving to the load-locked/store-conditional instructions LDREX and STREX. + +ARMv7 multiprocessing extensions introduce the ability to disable these +instructions, triggering an undefined instruction exception when executed. +Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB +sequence. If a memory access fault (an abort) occurs, a segmentation fault is +signalled to the triggering process. + +/proc/cpu/swp_emulation holds some statistics/information, including the PID of +the last process to trigger the emulation to be invocated. For example:: + + Emulated SWP: 12 + Emulated SWPB: 0 + Aborted SWP{B}: 1 + Last process: 314 + + +NOTE: + when accessing uncached shared regions, LDREX/STREX rely on an external + transaction monitoring block called a global monitor to maintain update + atomicity. If your system does not implement a global monitor, this option can + cause programs that perform SWP operations to uncached memory to deadlock, as + the STREX operation will always fail. |