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Date: Wed, 14 Feb 2007 16:38:46 +1100 From: Rusty Russell <rusty@...tcorp.com.au> To: Zachary Amsden <zach@...are.com> Cc: Jeremy Fitzhardinge <jeremy@...p.org>, Andrew Morton <akpm@...l.org>, xen-devel@...ts.xensource.com, Ian Pratt <ian.pratt@...source.com>, virtualization@...ts.osdl.org, linux-kernel@...r.kernel.org, Chris Wright <chrisw@...s-sol.org>, Andi Kleen <ak@....de>, Christian Limpach <Christian.Limpach@...cam.ac.uk> Subject: Re: [Xen-devel] Re: [patch 13/21] Xen-paravirt: Add nosegneg capability to the vsyscall page notes On Tue, 2007-02-13 at 14:45 -0800, Zachary Amsden wrote: > Jeremy Fitzhardinge wrote: > > Add the "nosegneg" fake capabilty to the vsyscall page notes. This is > > used by the runtime linker to select a glibc version which then > > disables negative-offset accesses to the thread-local segment via > > %gs. These accesses require emulation in Xen (because segments are > > truncated to protect the hypervisor address space) and avoiding them > > provides a measurable performance boost. > > > > I don't like this because now a kernel compiled with both CONFIG_XEN and > CONFIG_VMI has "nosegneg" turned on. We don't actually require this for > performance or correctness, so it would be nice to be able to > dynamically turn it off instead of having it forced. Ditto for lguest. Rusty. - 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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