[IA64] On return from syscall, hint b7 with __kernel_syscall_via_epc(). (96e01749) · Commits · 戴 / test

Why is this a good idea? Clearing b7 to 0 is guaranteed to do us no good and writing it with __kernel_syscall_via_epc() yields a 6 cycle improvement _if_ the application performs another EPC-based system- call without overwriting b7, which is not all that uncommon. Well worth the minimal cost of 1 bundle of code. Signed-off-by:

David Mosberger-Tang <davidm@hpl.hp.com> Signed-off-by:

Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/entry.S

+8 −1

Original line number	Diff line number	Diff line
		@@ -692,7 +692,7 @@ ENTRY(ia64_leave_syscall)
		;;
		(p6) ld4 r31=[r18] // load current_thread_info()->flags
		ld8 r19=[r2],PT(B6)-PT(LOADRS) // load ar.rsc value for "loadrs"
		mov b7=r0 // clear b7
		nop.i 0
		;;
		ld8 r23=[r3],PT(R11)-PT(AR_BSPSTORE) // load ar.bspstore (may be garbage)
		ld8 r18=[r2],PT(R9)-PT(B6) // load b6
		@@ -754,7 +754,14 @@ ENTRY(ia64_leave_syscall)
		(pUStk) ld4 r17=[r3] // r17 = cpu_data->phys_stacked_size_p8
		mov.m ar.csd=r0 // M2 clear ar.csd
		mov f10=f0 // clear f10

		nop.m 0
		movl r14=__kernel_syscall_via_epc // X
		;;
		nop.m 0
		nop.m 0
		mov b7=r14 // I0 clear b7 (hint with __kernel_syscall_via_epc)

		mov r14=r0 // clear r14
		mov f11=f0 // clear f11
		(pKStk) br.cond.dpnt.many skip_rbs_switch

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