From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 26721 invoked by alias); 8 Apr 2005 18:19:32 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 26675 invoked by uid 48); 8 Apr 2005 18:19:27 -0000 Date: Fri, 08 Apr 2005 18:19:00 -0000 Message-ID: <20050408181927.26674.qmail@sourceware.org> From: "law at redhat dot com" To: gcc-bugs@gcc.gnu.org In-Reply-To: <20050206175258.19794.kazu@cs.umass.edu> References: <20050206175258.19794.kazu@cs.umass.edu> Reply-To: gcc-bugzilla@gcc.gnu.org Subject: [Bug tree-optimization/19794] [meta-bug] Jump threading related bugs X-Bugzilla-Reason: CC X-SW-Source: 2005-04/txt/msg01038.txt.bz2 List-Id: ------- Additional Comments From law at redhat dot com 2005-04-08 18:19 ------- OK. I'm pretty sure the perl improvements are really just an artifact of changes in what objects get spilled onto the stack on the offsets of each particular object. I can with a small amount of work twiddle register allocation (and thus spilling behavior) in such a way as to make perl built without the threading changes run significantly faster than perl built with the threading changes. [ Which is the exact opposite of the runtime behavior if we do not twiddle the register allocation priorities. ] While it's certainly not proof, I'm confident that the reason performance is swinging back and forth is due to cache effects in the stack, particuliarly for spill slots in one critical function. Anything which changes which objects are spilled on the stack, or the offsets of those objects on the stack is likely to cause wild swings in performance, at least on P4s. The net result is, IMHO, we should ignore Perl's results when benchmarking the new threading changes on P4s, and possibly other platforms. This may also hold true when benchmarking other changes which could potentially affect register allocation (which, of course, is just about everything). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19794