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authorDavid Vrabel <david.vrabel@citrix.com>2012-07-09 11:39:08 +0100
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2012-07-19 15:51:57 -0400
commit1c32cdc633c96a14cca35de9db19338354c25111 (patch)
tree6a1e9df672d3aa8794bf197037be01ef1b34383c /drivers/xen
parent59290362da587ce2e6d2f4a7f85e362fa2d7fd39 (diff)
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xen/x86: avoid updating TLS descriptors if they haven't changed
When switching tasks in a Xen PV guest, avoid updating the TLS descriptors if they haven't changed. This improves the speed of context switches by almost 10% as much of the time the descriptors are the same or only one is different. The descriptors written into the GDT by Xen are modified from the values passed in the update_descriptor hypercall so we keep shadow copies of the three TLS descriptors to compare against. lmbench3 test Before After Improvement -------------------------------------------- lat_ctx -s 32 24 7.19 6.52 9% lat_pipe 12.56 11.66 7% Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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