From a1df417e74aa6dae7352dc8cbb0ad471af5b7c69 Mon Sep 17 00:00:00 2001 From: "Michael J. Chudobiak" Date: Mon, 25 Apr 2016 10:00:44 -0400 Subject: initial Olimex linux tree from Daniel, originally Feb 3, 2016 --- linux/Documentation/arm/swp_emulation | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) create mode 100644 linux/Documentation/arm/swp_emulation (limited to 'linux/Documentation/arm/swp_emulation') diff --git a/linux/Documentation/arm/swp_emulation b/linux/Documentation/arm/swp_emulation new file mode 100644 index 00000000..af903d22 --- /dev/null +++ b/linux/Documentation/arm/swp_emulation @@ -0,0 +1,27 @@ +Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE) +--------------------------------------------------------------------- + +ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommeds +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. + -- cgit