* Naveen N. Rao <naveen.n....@linux.vnet.ibm.com> wrote (on 2017-10-06 09:28:30 +0000):
> On 2017/09/18 09:23AM, Santosh Sivaraj wrote: > > 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 time > > with and without vDSO support. > > > > (Non-coarse clocks are also included just for completion) > > > > Without vDSO support: > > -------------------- > > clock-gettime-realtime: syscall: 172 nsec/call > > clock-gettime-realtime: libc: 26 nsec/call > > clock-gettime-realtime: vdso: 21 nsec/call > > clock-gettime-monotonic: syscall: 170 nsec/call > > clock-gettime-monotonic: libc: 30 nsec/call > > clock-gettime-monotonic: vdso: 24 nsec/call > > clock-gettime-realtime-coarse: syscall: 153 nsec/call > > clock-gettime-realtime-coarse: libc: 15 nsec/call > > clock-gettime-realtime-coarse: vdso: 9 nsec/call > > clock-gettime-monotonic-coarse: syscall: 167 nsec/call > > clock-gettime-monotonic-coarse: libc: 15 nsec/call > > clock-gettime-monotonic-coarse: vdso: 11 nsec/call > > > > CC: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > Signed-off-by: Santosh Sivaraj <sant...@fossix.org> > > --- > > arch/powerpc/kernel/asm-offsets.c | 2 ++ > > arch/powerpc/kernel/vdso64/gettimeofday.S | 56 > > +++++++++++++++++++++++++++++++ > > 2 files changed, 58 insertions(+) > > > > diff --git a/arch/powerpc/kernel/asm-offsets.c > > b/arch/powerpc/kernel/asm-offsets.c > > index 8cfb20e38cfe..b55c68c54dc1 100644 > > --- a/arch/powerpc/kernel/asm-offsets.c > > +++ b/arch/powerpc/kernel/asm-offsets.c > > @@ -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); > > > > diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S > > b/arch/powerpc/kernel/vdso64/gettimeofday.S > > index a0b4943811db..bae197a81add 100644 > > --- a/arch/powerpc/kernel/vdso64/gettimeofday.S > > +++ b/arch/powerpc/kernel/vdso64/gettimeofday.S > > @@ -71,6 +71,11 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) > > cror cr0*4+eq,cr0*4+eq,cr1*4+eq > > beq cr0,49f > > > > + cmpwi cr0,r3,CLOCK_REALTIME_COARSE > > + cmpwi cr1,r3,CLOCK_MONOTONIC_COARSE > > + cror cr0*4+eq,cr0*4+eq,cr1*4+eq > > + beq cr0,65f > > If you use cr5-7 here, you should be able to re-organize this to not > have to update r4/r11/r12 if we're taking the syscall path. Not > necessarily a huge win by itself, but can also help reuse some of the > other code between the _COARSE and the regular variants. > If we are going to use cr5-7, then the first patch is no longer required, we don't have to do a re-org of the intial clock_id checks. I will send the updated patch. Thanks, Santosh > - Naveen > > > + > > b 99f /* Fallback to syscall */ > > .cfi_register lr,r12 > > 49: bl V_LOCAL_FUNC(__get_datapage) /* get data page */ > > @@ -112,6 +117,57 @@ V_FUNCTION_BEGIN(__kernel_clock_gettime) > > 1: bge cr1,80f > > addi r4,r4,-1 > > add r5,r5,r7 > > + b 80f > > + > > + /* > > + * 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. > > + */ > > +65: bl V_LOCAL_FUNC(__get_datapage) /* get data page */ > > +70: ld r8,CFG_TB_UPDATE_COUNT(r3) > > + andi. r0,r8,1 /* pending update ? loop */ > > + bne- 70b > > + xor r0,r8,r8 /* create dependency */ > > + add r3,r3,r0 > > + > > + /* > > + * 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 cr1,78f > > + > > + /* CLOCK_MONOTONIC_COARSE */ > > + lwa r6,WTOM_CLOCK_SEC(r3) > > + lwa r9,WTOM_CLOCK_NSEC(r3) > > + > > + /* check if counter has updated */ > > +78: or r0,r6,r9 > > + 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 cr1,80f > > + > > + /* Add wall->monotonic offset and check for overflow or underflow */ > > + 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) > > -- > > 2.13.5 > > > --
