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Commit 5c929885 authored by Santosh Sivaraj's avatar Santosh Sivaraj Committed by Michael Ellerman
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powerpc/vdso64: Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE 



Current vDSO64 implementation does not have support for coarse clocks
(CLOCK_MONOTONIC_COARSE, CLOCK_REALTIME_COARSE), for which it falls back
to system call, increasing the response time, vDSO implementation reduces
the cycle time. Below is a benchmark of the difference in execution times.

(Non-coarse clocks are also included just for completion)

clock-gettime-realtime: syscall: 172 nsec/call
clock-gettime-realtime:    libc: 28 nsec/call
clock-gettime-realtime:    vdso: 22 nsec/call
clock-gettime-monotonic: syscall: 171 nsec/call
clock-gettime-monotonic:    libc: 30 nsec/call
clock-gettime-monotonic:    vdso: 25 nsec/call
clock-gettime-realtime-coarse: syscall: 153 nsec/call
clock-gettime-realtime-coarse:    libc: 16 nsec/call
clock-gettime-realtime-coarse:    vdso: 10 nsec/call
clock-gettime-monotonic-coarse: syscall: 167 nsec/call
clock-gettime-monotonic-coarse:    libc: 17 nsec/call
clock-gettime-monotonic-coarse:    vdso: 11 nsec/call

CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: default avatarNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: default avatarSantosh Sivaraj <santosh@fossix.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent f0200c02

arch/powerpc/kernel/asm-offsets.c

+2 −0
Original line number Diff line number Diff line
@@ -396,6 +396,8 @@ int main(void) 
	/* Other bits used by the vdso */

	DEFINE(CLOCK_REALTIME, CLOCK_REALTIME);

	DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC);

	DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE);

	DEFINE(CLOCK_MONOTONIC_COARSE, CLOCK_MONOTONIC_COARSE);

	DEFINE(NSEC_PER_SEC, NSEC_PER_SEC);

	DEFINE(CLOCK_REALTIME_RES, MONOTONIC_RES_NSEC);

arch/powerpc/kernel/vdso64/gettimeofday.S

+56 −11
Original line number Diff line number Diff line
@@ -64,6 +64,12 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) 
	cmpwi	cr0,r3,CLOCK_REALTIME

	cmpwi	cr1,r3,CLOCK_MONOTONIC

	cror	cr0*4+eq,cr0*4+eq,cr1*4+eq



	cmpwi	cr5,r3,CLOCK_REALTIME_COARSE

	cmpwi	cr6,r3,CLOCK_MONOTONIC_COARSE

	cror	cr5*4+eq,cr5*4+eq,cr6*4+eq



	cror	cr0*4+eq,cr0*4+eq,cr5*4+eq

	bne	cr0,99f



	mflr	r12			/* r12 saves lr */
@@ -72,6 +78,7 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) 
	bl	V_LOCAL_FUNC(__get_datapage)	/* get data page */

	lis	r7,NSEC_PER_SEC@h	/* want nanoseconds */

	ori	r7,r7,NSEC_PER_SEC@l

	beq	cr5,70f

50:	bl	V_LOCAL_FUNC(__do_get_tspec)	/* get time from tb & kernel */

	bne	cr1,80f			/* if not monotonic, all done */
@@ -97,17 +104,55 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) 
	ld	r0,CFG_TB_UPDATE_COUNT(r3)

        cmpld   cr0,r0,r8		/* check if updated */

	bne-	50b

	b	78f



	/* Add wall->monotonic offset and check for overflow or underflow.

	/*

	 * For coarse clocks we get data directly from the vdso data page, so

	 * we don't need to call __do_get_tspec, but we still need to do the

	 * counter trick.

	 */

	add	r4,r4,r6

70:	ld      r8,CFG_TB_UPDATE_COUNT(r3)

	andi.   r0,r8,1                 /* pending update ? loop */

	bne-    70b

	add     r3,r3,r0		/* r0 is already 0 */



	/*

	 * CLOCK_REALTIME_COARSE, below values are needed for MONOTONIC_COARSE

	 * too

	 */

	ld      r4,STAMP_XTIME+TSPC64_TV_SEC(r3)

	ld      r5,STAMP_XTIME+TSPC64_TV_NSEC(r3)

	bne     cr6,75f



	/* CLOCK_MONOTONIC_COARSE */

	lwa     r6,WTOM_CLOCK_SEC(r3)

	lwa     r9,WTOM_CLOCK_NSEC(r3)



	/* check if counter has updated */

	or      r0,r6,r9

75:	or	r0,r0,r4

	or	r0,r0,r5

	xor     r0,r0,r0

	add     r3,r3,r0

	ld      r0,CFG_TB_UPDATE_COUNT(r3)

	cmpld   cr0,r0,r8               /* check if updated */

	bne-    70b



	/* Counter has not updated, so continue calculating proper values for

	 * sec and nsec if monotonic coarse, or just return with the proper

	 * values for realtime.

	 */

	bne     cr6,80f



	/* Add wall->monotonic offset and check for overflow or underflow */

78:	add     r4,r4,r6

	add     r5,r5,r9

	cmpd    cr0,r5,r7

	cmpdi   cr1,r5,0

	blt	1f

	blt     79f

	subf    r5,r7,r5

	addi    r4,r4,1

1:	bge	cr1,80f

79:	bge     cr1,80f

	addi    r4,r4,-1

	add     r5,r5,r7