Subject: Re: [PATCH] powerpc: Fix bug where perf_counters breaks oprofile

From: Maynard Johnson <[email-masked]>
Date: Wed, 09 Sep 2009 08:31:39 -0500

Paul Mackerras wrote:
> Currently there is a bug where if you use oprofile on a pSeries
> machine, then use perf_counters, then use oprofile again, oprofile
> will not work correctly; it will lose the PMU configuration the next
> time the hypervisor does a partition context switch, and thereafter
> won't count anything.
> 
> Maynard Johnson identified the sequence causing the problem:
> - oprofile setup calls ppc_enable_pmcs(), which calls
>   pseries_lpar_enable_pmcs, which tells the hypervisor that we want
>   to use the PMU, and sets the "PMU in use" flag in the lppaca.
>   This flag tells the hypervisor whether it needs to save and restore
>   the PMU config.
> - The perf_counter code sets and clears the "PMU in use" flag directly
>   as it context-switches the PMU between tasks, and leaves it clear
>   when it finishes.
> - oprofile setup, called for a new oprofile run, calls ppc_enable_pmcs,
>   which does nothing because it has already been called.  In particular
>   it doesn't set the "PMU in use" flag.
> 
> This fixes the problem by arranging for ppc_enable_pmcs to always set
> the "PMU in use" flag.  It makes the perf_counter code call
> ppc_enable_pmcs also rather than calling the lower-level function
> directly, and removes the setting of the "PMU in use" flag from
> pseries_lpar_enable_pmcs, since that is now done in its caller.
> 
> This also removes the declaration of pasemi_enable_pmcs because it
> isn't defined anywhere.
Thanks, Paul.  I tested the patch, and oprofile and perf now play nicely together.

-Maynard
> 
> Reported-by: Maynard Johnson <[email-masked]>
> Signed-off-by: Paul Mackerras <[email-masked]>
> ---
>  arch/powerpc/include/asm/pmc.h         |   16 ++++++++++++++--
>  arch/powerpc/kernel/perf_counter.c     |   13 +++----------
>  arch/powerpc/kernel/sysfs.c            |    3 +++
>  arch/powerpc/platforms/pseries/setup.c |    4 ----
>  4 files changed, 20 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pmc.h b/arch/powerpc/include/asm/pmc.h
> index d6a616a..ccc68b5 100644
> --- a/arch/powerpc/include/asm/pmc.h
> +++ b/arch/powerpc/include/asm/pmc.h
> @@ -27,10 +27,22 @@ extern perf_irq_t perf_irq;
> 
>  int reserve_pmc_hardware(perf_irq_t new_perf_irq);
>  void release_pmc_hardware(void);
> +void ppc_enable_pmcs(void);
> 
>  #ifdef CONFIG_PPC64
> -void power4_enable_pmcs(void);
> -void pasemi_enable_pmcs(void);
> +#include <asm/lppaca.h>
> +
> +static inline void ppc_set_pmu_inuse(int inuse)
> +{
> +	get_lppaca()->pmcregs_in_use = inuse;
> +}
> +
> +extern void power4_enable_pmcs(void);
> +
> +#else /* CONFIG_PPC64 */
> +
> +static inline void ppc_set_pmu_inuse(int inuse) { }
> +
>  #endif
> 
>  #endif /* __KERNEL__ */
> diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
> index 70e1f57..ccd6b21 100644
> --- a/arch/powerpc/kernel/perf_counter.c
> +++ b/arch/powerpc/kernel/perf_counter.c
> @@ -62,7 +62,6 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
>  {
>  	return 0;
>  }
> -static inline void perf_set_pmu_inuse(int inuse) { }
>  static inline void perf_get_data_addr(struct pt_regs *regs, u64 *addrp) { }
>  static inline u32 perf_get_misc_flags(struct pt_regs *regs)
>  {
> @@ -93,11 +92,6 @@ static inline unsigned long perf_ip_adjust(struct pt_regs *regs)
>  	return 0;
>  }
> 
> -static inline void perf_set_pmu_inuse(int inuse)
> -{
> -	get_lppaca()->pmcregs_in_use = inuse;
> -}
> -
>  /*
>   * The user wants a data address recorded.
>   * If we're not doing instruction sampling, give them the SDAR
> @@ -531,8 +525,7 @@ void hw_perf_disable(void)
>  		 * Check if we ever enabled the PMU on this cpu.
>  		 */
>  		if (!cpuhw->pmcs_enabled) {
> -			if (ppc_md.enable_pmcs)
> -				ppc_md.enable_pmcs();
> +			ppc_enable_pmcs();
>  			cpuhw->pmcs_enabled = 1;
>  		}
> 
> @@ -594,7 +587,7 @@ void hw_perf_enable(void)
>  		mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
>  		mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
>  		if (cpuhw->n_counters == 0)
> -			perf_set_pmu_inuse(0);
> +			ppc_set_pmu_inuse(0);
>  		goto out_enable;
>  	}
> 
> @@ -627,7 +620,7 @@ void hw_perf_enable(void)
>  	 * bit set and set the hardware counters to their initial values.
>  	 * Then unfreeze the counters.
>  	 */
> -	perf_set_pmu_inuse(1);
> +	ppc_set_pmu_inuse(1);
>  	mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
>  	mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
>  	mtspr(SPRN_MMCR0, (cpuhw->mmcr[0] & ~(MMCR0_PMC1CE | MMCR0_PMCjCE))
> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> index f41aec8..956ab33 100644
> --- a/arch/powerpc/kernel/sysfs.c
> +++ b/arch/powerpc/kernel/sysfs.c
> @@ -17,6 +17,7 @@
>  #include <asm/prom.h>
>  #include <asm/machdep.h>
>  #include <asm/smp.h>
> +#include <asm/pmc.h>
> 
>  #include "cacheinfo.h"
> 
> @@ -123,6 +124,8 @@ static DEFINE_PER_CPU(char, pmcs_enabled);
> 
>  void ppc_enable_pmcs(void)
>  {
> +	ppc_set_pmu_inuse(1);
> +
>  	/* Only need to enable them once */
>  	if (__get_cpu_var(pmcs_enabled))
>  		return;
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index 8d75ea2..ca5f2e1 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -223,10 +223,6 @@ static void pseries_lpar_enable_pmcs(void)
>  	set = 1UL << 63;
>  	reset = 0;
>  	plpar_hcall_norets(H_PERFMON, set, reset);
> -
> -	/* instruct hypervisor to maintain PMCs */
> -	if (firmware_has_feature(FW_FEATURE_SPLPAR))
> -		get_lppaca()->pmcregs_in_use = 1;
>  }
> 
>  static void __init pseries_discover_pic(void)