diff options
| author | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2015-09-25 14:34:24 +0200 |
|---|---|---|
| committer | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2015-09-28 13:56:57 +0200 |
| commit | 258ad71e9626c16f30b40e06c321326636c976ff (patch) | |
| tree | da6e210947d590159796434bf04cf364247ac20a /c/src/lib/libcpu/powerpc/new-exceptions | |
| parent | SMP: Simplify thread lock operations (diff) | |
| download | rtems-258ad71e9626c16f30b40e06c321326636c976ff.tar.bz2 | |
SMP: Fix and optimize thread dispatching
According to the C11 and C++11 memory models only a read-modify-write
operation guarantees that we read the last value written in modification
order. Avoid the sequential consistent thread fence and instead use the
inter-processor interrupt to set the thread dispatch necessary
indicator.
Diffstat (limited to 'c/src/lib/libcpu/powerpc/new-exceptions')
| -rw-r--r-- | c/src/lib/libcpu/powerpc/new-exceptions/cpu_asm.S | 25 |
1 files changed, 11 insertions, 14 deletions
diff --git a/c/src/lib/libcpu/powerpc/new-exceptions/cpu_asm.S b/c/src/lib/libcpu/powerpc/new-exceptions/cpu_asm.S index 5d8c70d290..8bfef20043 100644 --- a/c/src/lib/libcpu/powerpc/new-exceptions/cpu_asm.S +++ b/c/src/lib/libcpu/powerpc/new-exceptions/cpu_asm.S @@ -413,12 +413,12 @@ check_is_executing: addi r6, r5, PPC_CONTEXT_OFFSET_IS_EXECUTING lwarx r7, r0, r6 cmpwi r7, 0 - bne check_thread_dispatch_necessary + bne get_potential_new_heir /* Try to update the is executing indicator of the heir context */ li r7, 1 stwcx. r7, r0, r6 - bne check_thread_dispatch_necessary + bne get_potential_new_heir isync #endif @@ -536,26 +536,23 @@ PROC (_CPU_Context_restore): b restore_context #ifdef RTEMS_SMP -check_thread_dispatch_necessary: +get_potential_new_heir: GET_SELF_CPU_CONTROL r6 - /* Check if a thread dispatch is necessary */ - lbz r7, PER_CPU_DISPATCH_NEEDED(r6) - cmpwi r7, 0 - beq check_is_executing - - /* We have a new heir */ - - /* Clear the thread dispatch necessary flag */ - li r7, 0 - stb r7, PER_CPU_DISPATCH_NEEDED(r6) - msync + /* We may have a new heir */ /* Read the executing and heir */ lwz r7, PER_CPU_OFFSET_EXECUTING(r6) lwz r8, PER_CPU_OFFSET_HEIR(r6) + /* + * Update the executing only if necessary to avoid cache line + * monopolization. + */ + cmpw r7, r8 + beq check_is_executing + /* Calculate the heir context pointer */ sub r7, r4, r7 add r4, r8, r7 |