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Commit 837e72f7 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64: Drop reservation-clearing ldarx in context switch 



There is no need to explicitly break the reservation in _switch,
because we are guaranteed that the context switch path will include a
larx/stcx.

Comment the guarantee and remove the reservation clear from _switch.

This is worth 1-2% in context switch performance.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent e4c0fc5f

arch/powerpc/kernel/entry_64.S

+3 −8
Original line number Diff line number Diff line
@@ -521,15 +521,10 @@ _GLOBAL(_switch) 
#endif /* CONFIG_SMP */



	/*

	 * If we optimise away the clear of the reservation in system

	 * calls because we know the CPU tracks the address of the

	 * reservation, then we need to clear it here to cover the

	 * case that the kernel context switch path has no larx

	 * instructions.

	 * The kernel context switch path must contain a spin_lock,

	 * which contains larx/stcx, which will clear any reservation

	 * of the task being switched.

	 */

BEGIN_FTR_SECTION

	ldarx	r6,0,r1

END_FTR_SECTION_IFSET(CPU_FTR_STCX_CHECKS_ADDRESS)



BEGIN_FTR_SECTION

/*