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xen-devel
[Xen-devel] Re: [patch 13/21] Xen-paravirt: Add nosegneg capability to t
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To: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
[Xen-devel] Re: [patch 13/21] Xen-paravirt: Add nosegneg capability to the vsyscall page notes |
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From: |
Zachary Amsden <zach@xxxxxxxxxx> |
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Date: |
Thu, 15 Feb 2007 22:06:37 -0800 |
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Cc: |
xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Andi Kleen <ak@xxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx> |
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Thu, 15 Feb 2007 22:06:09 -0800 |
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Thunderbird 1.5.0.9 (X11/20061206) |
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.
Signed-off-by: Ian Pratt <ian.pratt@xxxxxxxxxxxxx>
Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Acked-by: Zachary Amsden <zach@xxxxxxxxxx>
We would like to see this by dynamic, but that is much more difficult to
achieve, and seeing your recent linker issues, I don't think this should
gate merging this code. The performance loss for us I believe to be
negligible, and the fix is quite a bit more complicated than something
achievable in the .21 timeframe.
Zach
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