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Commit 70929a57 authored by David Mosberger-Tang's avatar David Mosberger-Tang Committed by Tony Luck
Browse files

[IA64] Reschedule __kernel_syscall_via_epc(). 



Avoid some stalls, which is good for about 2 cycles when invoking a
light-weight handler.  When invoking a heavy-weight handler, this
helps by about 7 cycles, with most of the improvement coming from the
improved branch-prediction achieved by splitting the BBB bundle into
two MIB bundles.

Signed-off-by: default avatarDavid Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent f8fa5448

arch/ia64/kernel/gate.S

+18 −13
Original line number Diff line number Diff line
@@ -79,31 +79,34 @@ GLOBAL_ENTRY(__kernel_syscall_via_epc) 
	;;

	rsm psr.be // note: on McKinley "rsm psr.be/srlz.d" is slightly faster than "rum psr.be"

	LOAD_FSYSCALL_TABLE(r14)



	;;

	mov r16=IA64_KR(CURRENT)		// 12 cycle read latency

	tnat.nz p10,p9=r15

	shladd r18=r17,3,r14

	mov r19=NR_syscalls-1

	;;

	shladd r18=r17,3,r14



	srlz.d

	cmp.ne p8,p0=r0,r0			// p8 <- FALSE

	lfetch [r18]				// M0|1

	mov r29=psr				// read psr (12 cyc load latency)

	/* Note: if r17 is a NaT, p6 will be set to zero.  */

	cmp.geu p6,p7=r19,r17			// (syscall > 0 && syscall < 1024+NR_syscalls)?

	;;

(p6)	ld8 r18=[r18]

	mov r21=ar.fpsr

	add r14=-8,r14				// r14 <- addr of fsys_bubble_down entry

	tnat.nz p10,p9=r15

	mov r26=ar.pfs

	;;

	srlz.d

(p6)	ld8 r18=[r18]

	nop.i 0

	;;

	nop.m 0

(p6)	mov b7=r18

(p6)	tbit.z p8,p0=r18,0

(p6)	tbit.z.unc p8,p0=r18,0



	nop.m 0

	nop.i 0

(p8)	br.dptk.many b7



(p6)	rsm psr.i

	mov r27=ar.rsc

	mov r26=ar.pfs

	;;

	mov r29=psr				// read psr (12 cyc load latency)

(p6)	rsm psr.i

/*

 * brl.cond doesn't work as intended because the linker would convert this branch

 * into a branch to a PLT.  Perhaps there will be a way to avoid this with some
@@ -111,6 +114,8 @@ GLOBAL_ENTRY(__kernel_syscall_via_epc) 
 * instead.

 */

#ifdef CONFIG_ITANIUM

	add r14=-8,r14				// r14 <- addr of fsys_bubble_down entry

	;;

(p6)	ld8 r14=[r14]				// r14 <- fsys_bubble_down

	;;

(p6)	mov b7=r14