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Message-Id: <1184633155.5955.29.camel@localhost.localdomain>
Date: Tue, 17 Jul 2007 10:45:55 +1000
From: Rusty Russell <rusty@...tcorp.com.au>
To: Jeremy Fitzhardinge <jeremy@...source.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.com>,
Zachary Amsden <zach@...are.com>,
Jeremy Fitzhardinge <jeremy@...p.org>,
Xen-devel <xen-devel@...ts.xensource.com>,
Andi Kleen <ak@...e.de>, lkml <linux-kernel@...r.kernel.org>,
Chris Wright <chrisw@...s-sol.org>,
Ian Pratt <ian.pratt@...source.com>,
Andrew Morton <akpm@...ux-foundation.com>,
Ulrich Drepper <drepper@...hat.com>,
Roland McGrath <roland@...hat.com>,
Christian Limpach <Christian.Limpach@...cam.ac.uk>
Subject: Re: [Xen-devel] [patch 17/44] Add nosegneg capability to the
vsyscall page notes
On Mon, 2007-07-16 at 16:15 -0700, Jeremy Fitzhardinge wrote:
> plain text document attachment (xen-vsyscall-note.patch)
> 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.
Hmm, this is still unconditional? Not that it causes any measurable
slowdown when enabled, but ISTR discussing making this dynamic...
Rusty.
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