linux-kernel - Re: [PATCH v5 1/3] arm64: perf: Include threshold control fields in PMEVTYPER mask

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Date:   Wed, 22 Nov 2023 14:14:52 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     James Clark <james.clark@....com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, suzuki.poulose@....com,
        will@...nel.org, mark.rutland@....com
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] arm64: perf: Include threshold control fields in
 PMEVTYPER mask



On 11/13/23 16:55, James Clark wrote:
> FEAT_PMUv3_TH (Armv8.8) adds two new fields to PMEVTYPER, so include
> them in the mask. These aren't writable on 32 bit kernels as they are in
> the high part of the register, so only include them for arm64.
> 
> It would be difficult to do this statically in the asm header files for
> each platform without resulting in circular includes or #ifdefs inline
> in the code. For that reason the ARMV8_PMU_EVTYPE_MASK definition has
> been removed and the mask is constructed programmatically.

Agreed, and this also makes sense because there is just a single instance
for ARMV8_PMU_EVTYPE_MASK in armv8pmu_write_evtype().

> 
> Signed-off-by: James Clark <james.clark@....com>
> ---
>  drivers/perf/arm_pmuv3.c       | 9 ++++++++-
>  include/linux/perf/arm_pmuv3.h | 3 ++-
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> index 6ca7be05229c..1d40d794f5e4 100644
> --- a/drivers/perf/arm_pmuv3.c
> +++ b/drivers/perf/arm_pmuv3.c
> @@ -555,8 +555,15 @@ static void armv8pmu_write_counter(struct perf_event *event, u64 value)
>  static inline void armv8pmu_write_evtype(int idx, u32 val)
>  {
>  	u32 counter = ARMV8_IDX_TO_COUNTER(idx);
> +	unsigned long mask = ARMV8_PMU_EVTYPE_EVENT |
> +			     ARMV8_PMU_INCLUDE_EL2 |
> +			     ARMV8_PMU_EXCLUDE_EL0 |
> +			     ARMV8_PMU_EXCLUDE_EL1;

At first this looks bit odd sequence - EL2, EL0, EL1 but such as these
bit positions.

#define ARMV8_PMU_EXCLUDE_EL1           (1U << 31)
#define ARMV8_PMU_EXCLUDE_EL0           (1U << 30)
#define ARMV8_PMU_INCLUDE_EL2           (1U << 27)

>  
> -	val &= ARMV8_PMU_EVTYPE_MASK;
> +	if (IS_ENABLED(CONFIG_ARM64))
> +		mask |= ARMV8_PMU_EVTYPE_TC | ARMV8_PMU_EVTYPE_TH;

This makes sense.

> +
> +	val &= mask;
>  	write_pmevtypern(counter, val);
>  }
>  
> diff --git a/include/linux/perf/arm_pmuv3.h b/include/linux/perf/arm_pmuv3.h
> index 9c226adf938a..ddd1fec86739 100644
> --- a/include/linux/perf/arm_pmuv3.h
> +++ b/include/linux/perf/arm_pmuv3.h
> @@ -228,7 +228,8 @@
>  /*
>   * PMXEVTYPER: Event selection reg
>   */
> -#define ARMV8_PMU_EVTYPE_MASK	0xc800ffff	/* Mask for writable bits */
> +#define ARMV8_PMU_EVTYPE_TH	GENMASK(43, 32)
> +#define ARMV8_PMU_EVTYPE_TC	GENMASK(63, 61)

Looks correct.

>  #define ARMV8_PMU_EVTYPE_EVENT	0xffff		/* Mask for EVENT bits */
>  
>  /*

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>