One of the Summer of Code projects I proposed to the lispNYC which ended up not being funded was to investigate the effect of calling conventions on the x86 platform; my original proposal is still viewable at [1]. Since some of the work in that proposal has now been done, a report is due; this is probably the best place for it. Juho Snellman performed some investigations on code related to but separate from that which SBCL produces, and reported what he measured on his blog [2]; the executive summary is that, yes, the calling convention potentially makes a significant difference in performance of function call on current hardware: up to a factor of four (on code that doesn't do very much other than function calls :-). Some time later, Alastair Bridgewater had a spare couple of hours, so he actually came up with a patch [3] coming up with a different convention for one of the call types (specifically the "unknown-values" convention), as well as documentation for the internals manual [4]. This patch (as well as a similar one for the 64-bit x86-64 backend) was recently merged into SBCL's CVS; the automated build-and-benchmark machines have had some time to run, so I'll leave the interested parties to guess which revision incorporated the patch from inspecting one of the graphs [5]. There are other benchmarks in the Gabriel suite which test function call; TAK, in particular. The function call convention which SBCL uses there suffers from the same problem as the one Alastair changed (unpaired CALL/RET) but is sufficiently different that it did not get reimplemented in the same changeset. Christophe [1] <http://www.alphageeksinc.com/cgi-bin/lispnyc.cgi?SbclCallingConvention> [2] <http://jsnell.iki.fi/blog/archive/2005-10-12.html> [3] <http://article.gmane.org/gmane.lisp.steel-bank.devel/6439> [4] <http://www.sbcl.org/sbcl-internals/Calling-Convention.html> [5] <http://sbcl-test.boinkor.net/bench/?HOST=baker&IMPLEMENTATIONS=SBCL%2C%28%3AARCH+%3AEMULATED-X86+%3AFEATURES+NIL%29&IMPLEMENTATIONS=SBCL%2C%28%3AARCH+%3AX86_64+%3AFEATURES+NIL%29&ONLY-RELEASE=0.9.10#ACKERMANN>