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| author | Russell King <rmk+kernel@arm.linux.org.uk> | 2011-01-07 01:32:52 +0300 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2011-01-07 01:32:52 +0300 |
| commit | 4073723acb9cdcdbe4df9c0e0c376c65d1697e43 (patch) | |
| tree | f41c17eac157b1223ce104845cf9b1e5a9e6a83d /Documentation/arm/swp_emulation | |
| parent | 58daf18cdcab550262a5f4681e1f1e073e21965a (diff) | |
| parent | 4ec3eb13634529c0bc7466658d84d0bbe3244aea (diff) | |
| download | linux-4073723acb9cdcdbe4df9c0e0c376c65d1697e43.tar.xz | |
Merge branch 'misc' into devel
Conflicts:
arch/arm/Kconfig
arch/arm/common/Makefile
arch/arm/kernel/Makefile
arch/arm/kernel/smp.c
Diffstat (limited to 'Documentation/arm/swp_emulation')
| -rw-r--r-- | Documentation/arm/swp_emulation | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/arm/swp_emulation b/Documentation/arm/swp_emulation new file mode 100644 index 000000000000..af903d22fd93 --- /dev/null +++ b/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. + |