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powerpc: No need to save XER in a system call
authorAnton Blanchard <anton@samba.org>
Wed, 4 Apr 2012 18:24:29 +0000 (18:24 +0000)
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>
Mon, 30 Apr 2012 05:34:44 +0000 (15:34 +1000)
The XER is a volatile register so there is no need to save and restore
it over a system call - zero it out in the exception stack frame
instead.

This should fix a 5 cycle stall of the mfxer/std seen on POWER7.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

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