Subject: Re: [PATCH 2/2][v2] powerpc/perf: Sample only if SIAR-Valid bit is set in P7+

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 07 Sep 2012 10:50:23 +1000

On Mon, 2012-07-16 at 14:22 -0700, Sukadev Bhattiprolu wrote:
> From: Sukadev Bhattiprolu <[email-masked]>
> Date: Mon, 2 Jul 2012 08:06:14 -0700
> Subject: [PATCH 2/2][v2] powerpc/perf: Sample only if SIAR-Valid bit is set in P7+
> 
> On POWER7+ two new bits (mmcra[35] and mmcra[36]) indicate whether the
> contents of SIAR and SDAR are valid.
> 
> For marked instructions on P7+, we must save the contents of SIAR and
> SDAR registers only if these new bits are set.
> 
> This code/check for the SIAR-Valid bit is specific to P7+, so rather than
> waste a CPU-feature bit use the PVR flag.

This appears to be based on an ancient code base. The code has changed
significantly in that area and this patch doesn't apply at all.

I have applied the first patch and renamed PV_ to PVR_ since we've
renamed them all since then. This will show up in powerpc-next later
today. Please rebase your perf patch on top of that.

Cheers,
Ben.

> Note that Carl Love proposed a similar change for oprofile:
> 
>         https://lkml.org/lkml/2012/6/22/309
> 
> Changelog[v2]:
> 	- [Gabriel Paubert] Rename PV_POWER7P to PV_POWER7p.
> 
> Signed-off-by: Sukadev Bhattiprolu <[email-masked]>
> ---
>  arch/powerpc/include/asm/perf_event_server.h |    1 +
>  arch/powerpc/include/asm/reg.h               |    4 +++
>  arch/powerpc/perf/core-book3s.c              |   38 ++++++++++++++++++++++---
>  arch/powerpc/perf/power7-pmu.c               |    3 ++
>  4 files changed, 41 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/perf_event_server.h b/arch/powerpc/include/asm/perf_event_server.h
> index 078019b..9710be3 100644
> --- a/arch/powerpc/include/asm/perf_event_server.h
> +++ b/arch/powerpc/include/asm/perf_event_server.h
> @@ -49,6 +49,7 @@ struct power_pmu {
>  #define PPMU_ALT_SIPR		2	/* uses alternate posn for SIPR/HV */
>  #define PPMU_NO_SIPR		4	/* no SIPR/HV in MMCRA at all */
>  #define PPMU_NO_CONT_SAMPLING	8	/* no continuous sampling */
> +#define PPMU_SIAR_VALID		16	/* Processor has SIAR Valid bit */
>  
>  /*
>   * Values for flags to get_alternatives()
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index 65b6164..a7a9a8b 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -601,6 +601,10 @@
>  #define   POWER6_MMCRA_SIPR   0x0000020000000000ULL
>  #define   POWER6_MMCRA_THRM	0x00000020UL
>  #define   POWER6_MMCRA_OTHER	0x0000000EUL
> +
> +#define   POWER7P_MMCRA_SIAR_VALID 0x10000000	/* P7+ SIAR contents valid */
> +#define   POWER7P_MMCRA_SDAR_VALID 0x08000000	/* P7+ SDAR contents valid */
> +
>  #define SPRN_PMC1	787
>  #define SPRN_PMC2	788
>  #define SPRN_PMC3	789
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 8f84bcb..0a392d8 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -103,14 +103,20 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
>   * If we're not doing instruction sampling, give them the SDAR
>   * (sampled data address).  If we are doing instruction sampling, then
>   * only give them the SDAR if it corresponds to the instruction
> - * pointed to by SIAR; this is indicated by the [POWER6_]MMCRA_SDSYNC
> - * bit in MMCRA.
> + * pointed to by SIAR; this is indicated by the [POWER6_]MMCRA_SDSYNC or
> + * the [POWER7P_]MMCRA_SDAR_VALID bit in MMCRA.
>   */
>  static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp)
>  {
>  	unsigned long mmcra = regs->dsisr;
> -	unsigned long sdsync = (ppmu->flags & PPMU_ALT_SIPR) ?
> -		POWER6_MMCRA_SDSYNC : MMCRA_SDSYNC;
> +	unsigned long sdsync;
> +
> +	if (ppmu->flags & PPMU_SIAR_VALID)
> +		sdsync = POWER7P_MMCRA_SDAR_VALID;
> +	else if (ppmu->flags & PPMU_ALT_SIPR)
> +		sdsync = POWER6_MMCRA_SDSYNC;
> +	else
> +		sdsync = MMCRA_SDSYNC;
>  
>  	if (!(mmcra & MMCRA_SAMPLE_ENABLE) || (mmcra & sdsync))
>  		*addrp = mfspr(SPRN_SDAR);
> @@ -1248,6 +1254,25 @@ struct pmu power_pmu = {
>  	.event_idx	= power_pmu_event_idx,
>  };
>  
> +
> +/*
> + * On processors like P7+ that have the SIAR-Valid bit, marked instructions
> + * must be sampled only if the SIAR-valid bit is set.
> + *
> + * For unmarked instructions and for processors that don't have the SIAR-Valid
> + * bit, assume that SIAR is valid.
> + */
> +static inline int siar_valid(struct pt_regs *regs)
> +{
> +	unsigned long mmcra = regs->dsisr;
> +	int marked = mmcra & MMCRA_SAMPLE_ENABLE;
> +
> +	if ((ppmu->flags & PPMU_SIAR_VALID) && marked)
> +		return mmcra & POWER7P_MMCRA_SIAR_VALID;
> +
> +	return 1;
> +}
> +
>  /*
>   * A counter has overflowed; update its count and record
>   * things if requested.  Note that interrupts are hard-disabled
> @@ -1281,7 +1306,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
>  			left += period;
>  			if (left <= 0)
>  				left = period;
> -			record = 1;
> +			record = siar_valid(regs);
>  			event->hw.last_period = event->hw.sample_period;
>  		}
>  		if (left < 0x80000000LL)
> @@ -1340,6 +1365,9 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
>  	    !(mmcra & MMCRA_SAMPLE_ENABLE))
>  		return regs->nip;
>  
> +	if (!siar_valid(regs))
> +		return 0;	// no valid instruction pointer
> +
>  	return mfspr(SPRN_SIAR) + perf_ip_adjust(regs);
>  }
>  
> diff --git a/arch/powerpc/perf/power7-pmu.c b/arch/powerpc/perf/power7-pmu.c
> index 1251e4d..970a634 100644
> --- a/arch/powerpc/perf/power7-pmu.c
> +++ b/arch/powerpc/perf/power7-pmu.c
> @@ -373,6 +373,9 @@ static int __init init_power7_pmu(void)
>  	    strcmp(cur_cpu_spec->oprofile_cpu_type, "ppc64/power7"))
>  		return -ENODEV;
>  
> +	if (__is_processor(PV_POWER7p))
> +		power7_pmu.flags |= PPMU_SIAR_VALID;
> +
>  	return register_power_pmu(&power7_pmu);
>  }
>