From owner-freebsd-arch@FreeBSD.ORG Tue May 31 17:15:41 2005 Return-Path: X-Original-To: arch@freebsd.org Delivered-To: freebsd-arch@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id E4C6316A41C; Tue, 31 May 2005 17:15:41 +0000 (GMT) (envelope-from julian@elischer.org) Received: from mail.vicor-nb.com (bigwoop.vicor-nb.com [208.206.78.2]) by mx1.FreeBSD.org (Postfix) with ESMTP id B8F6143D4C; Tue, 31 May 2005 17:15:40 +0000 (GMT) (envelope-from julian@elischer.org) Received: from [208.206.78.97] (julian.vicor-nb.com [208.206.78.97]) by mail.vicor-nb.com (Postfix) with ESMTP id 73BF57A403; Tue, 31 May 2005 10:15:40 -0700 (PDT) Message-ID: <429C9BBC.1060108@elischer.org> Date: Tue, 31 May 2005 10:15:40 -0700 From: Julian Elischer User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.7) Gecko/20050423 X-Accept-Language: en, hu MIME-Version: 1.0 To: Robert Watson References: <20050528150815.X29776@fledge.watson.org> In-Reply-To: <20050528150815.X29776@fledge.watson.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: arch@freebsd.org, Suleiman Souhlal Subject: Re: [PATCH] Stackgap X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 31 May 2005 17:15:42 -0000 Stack gap can actually improve performance in some cases.. the cache for the base of teh stack can become overly flushed by the fact that all stacks start with the same offset from the page. making this random can actually help this. Robert Watson wrote: > > On Fri, 27 May 2005, Suleiman Souhlal wrote: > > In the past, substantial performance hits have been measured due to > poor stack alignment. Specifically, in combination with less optimal > compiler behavior, the results have been pretty nasty. Have you tried > micro-benchmarking a series of runs with this stack offset randomness > using floating point on stack arguments to see if there's a measurable > cost to moving the stack around? Hopefull if all is well, there will > be little or no difference, but a small error here could result in a > substantial performance hit... Stack gap can actually improve performance in some cases.. the cache for the base of teh stack can become overly flushed by the fact that all stacks start with the same offset from the page. making this random can actually help this. > > > Robert N M Watson > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org"