Hi Manfred,Thanks. The test app compares the time needed for three different short loops: a loop with six empty function calls, a loop with six function calls and one nop in the middle, and a loop with a "rep;nop;" in the middle.
I'm using unixware 7 but couldn't compile your source with native cc, I had to compile it with gcc.
here are the results:
Result:
- nop needs 0 cycles - executed in parallel.
- rep;nop between 24 and 60 cycles - long enough that the pipeline is emptied.
I've searched around for further info regarding the recommended spinlock algorithm:
- The optimization manual (google for "Intel 248966") contains a section about pause instructions: The memory ordering violation is from the multiple simultaneous reads that are executed due to pipelining the busy loop.
- It references the Application Note AP-949 "Using Spin-Loops on Intel Pentium 4 Processor and Intel Xeon Processor" for further details. Unfortunately the app notes are stored on cedar.intel.com, and that server appears to be down :-(
-- Manfred
---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ?
http://www.postgresql.org/docs/faqs/FAQ.html
