x86/pvops: add a paravirt_ident functions to allow special patching

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Impact: Optimization

Several paravirt ops implementations simply return their arguments,
the most obvious being the make_pte/pte_val class of operations on
native.

On 32-bit, the identity function is literally a no-op, as the calling
convention uses the same registers for the first argument and return.
On 64-bit, it can be implemented with a single "mov".

This patch adds special identity functions for 32 and 64 bit argument,
and machinery to recognize them and replace them with either nops or a
mov as appropriate.

At the moment, the only users for the identity functions are the
pagetable entry conversion functions.

The result is a measureable improvement on pagetable-heavy benchmarks
(2-3%, reducing the pvops overhead from 5 to 2%).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

...

This commit is contained in:

Jeremy Fitzhardinge 2009-01-28 14:35:02 -08:00 • committed by H. Peter Anvin

parent 319f3ba52c

commit 41edafdb78

4 changed files with 98 additions and 9 deletions

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5

arch/x86/include/asm/paravirt.h

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75

arch/x86/kernel/paravirt.c

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12

arch/x86/kernel/paravirt_patch_32.c

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15

arch/x86/kernel/paravirt_patch_64.c

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