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Date: Wed, 05 Oct 2011 17:17:09 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Jeremy Fitzhardinge <jeremy@...p.org> CC: Jason Baron <jbaron@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, "David S. Miller" <davem@...emloft.net>, David Daney <david.daney@...ium.com>, Michael Ellerman <michael@...erman.id.au>, Jan Glauber <jang@...ux.vnet.ibm.com>, the arch/x86 maintainers <x86@...nel.org>, Xen Devel <xen-devel@...ts.xensource.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>, peterz@...radead.org Subject: Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out On 10/05/2011 05:16 PM, Jeremy Fitzhardinge wrote: > On 10/04/2011 09:30 AM, H. Peter Anvin wrote: >> On 10/04/2011 07:10 AM, Jason Baron wrote: >>> 1) The jmp +0, is a 'safe' no-op that I know is going to initially >>> boot for all x86. I'm not sure if there is a 5-byte nop that works on >>> all x86 variants - but by using jmp +0, we make it much easier to debug >>> cases where we may be using broken no-ops. >>> >> There are *plenty*. jmp+0 is about as pessimal as you can get. > > As an aside, do you know if a 2-byte unconditional jmp is any more > efficient than 5-byte, aside from just being a smaller instruction and > taking less icache? > I don't know for sure, no. I probably depends on the CPU. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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