leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

powerpc/vdso64: Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE

Browse Source 
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: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Santosh Sivaraj <santosh@fossix.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Santosh Sivaraj 2017-10-16 11:19:14 +05:30 committed by Michael Ellerman
parent f0200c0288
commit 5c929885f1
2 changed files with 58 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/powerpc/kernel/asm-offsets.c
View File

@ -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);

67
arch/powerpc/kernel/vdso64/gettimeofday.S
View File

@ -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 */
@ -97,19 +104,57 @@ 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
add r5,r5,r9
cmpd cr0,r5,r7
cmpdi cr1,r5,0
blt 1f
subf r5,r7,r5
addi r4,r4,1
1: bge cr1,80f
addi r4,r4,-1
add r5,r5,r7
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 79f
subf r5,r7,r5
addi r4,r4,1
79: bge cr1,80f
addi r4,r4,-1
add r5,r5,r7
80: std r4,TSPC64_TV_SEC(r11)
std r5,TSPC64_TV_NSEC(r11)