Message-ID: <438B9372.2080309@zytor.com>
Date: Mon, 28 Nov 2005 15:32:02 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Zachary Amsden <zach@vmware.com>
CC: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>,
       Bill Davidsen <davidsen@tmr.com>, Linus Torvalds <torvalds@osdl.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Andi Kleen <ak@suse.de>,
       Gerd Knorr <kraxel@suse.de>, Dave Jones <davej@redhat.com>,
       Pavel Machek <pavel@ucw.cz>, Andrew Morton <akpm@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       Pratap Subrahmanyam <pratap@vmware.com>,
       Christopher Li <chrisl@vmware.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] SMP alternatives
References: <1132764133.7268.51.camel@localhost.localdomain> <20051123163906.GF20775@brahms.suse.de> <1132766489.7268.71.camel@localhost.localdomain> <Pine.LNX.4.64.0511230858180.13959@g5.osdl.org> <4384AECC.1030403@zytor.com> <Pine.LNX.4.64.0511231031350.13959@g5.osdl.org> <1132782245.13095.4.camel@localhost.localdomain> <Pine.LNX.4.64.0511231331040.13959@g5.osdl.org> <20051123214835.GA24044@nevyn.them.org> <Pine.LNX.4.64.0511231416490.13959@g5.osdl.org> <20051123222056.GA25078@nevyn.them.org> <Pine.LNX.4.64.0511231502250.13959@g5.osdl.org> <438B600C.1050604@tmr.com> <438B827A.2090609@wolfmountaingroup.com> <438B8BF8.4020604@vmware.com> <438B8DC6.8070006@zytor.com> <438B92FB.4060805@vmware.com>
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Zachary Amsden wrote:
> 
> I spoke silicon too heavy handedly.  The complexity of the issue 
> disappears if you take an exception, but rewinding state prior to the 
> exception and reissuing is going to be less efficient than getting it 
> right the first time, which is something software can always guarantee.  
> You need to add more hardware for prediction to get it right all the 
> time, and it is not clear the cost of that hardware is justified when 
> software can always do the right thing.
> 

Taking exceptions is fine as long as you don't do it too often.  I'm 
starting to suspect that the only way to do this right all the time is 
to have this be part of the page attributes, since it's region-specific.

	-hpa

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