linux-kernel - Re: [PATCH V4 2/6] csky: Add count-width property for csky pmu

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Date:   Tue, 4 Jun 2019 13:35:45 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Mao Han <han_mao@...ky.com>
Cc:     linux-kernel@...r.kernel.org, linux-csky@...r.kernel.org
Subject: Re: [PATCH V4 2/6] csky: Add count-width property for csky pmu

Hi Mao,

On Tue, Jun 4, 2019 at 10:25 AM Mao Han <han_mao@...ky.com> wrote:
>
> The csky pmu counter may have different io width. When the counter is
> smaller then 64 bits and counter value is smaller than the old value, it
> will result to a extremely large delta value. So the sampled value should
> be extend to 64 bits to avoid this, the extension bits base on the
> count-width property from dts.
>
> Signed-off-by: Mao Han <han_mao@...ky.com>
> Cc: Guo Ren <guoren@...nel.org>
> ---
>  arch/csky/kernel/perf_event.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/csky/kernel/perf_event.c b/arch/csky/kernel/perf_event.c
> index c022acc..36f7f20 100644
> --- a/arch/csky/kernel/perf_event.c
> +++ b/arch/csky/kernel/perf_event.c
> @@ -9,6 +9,7 @@
>  #include <linux/platform_device.h>
>
>  #define CSKY_PMU_MAX_EVENTS 32
> +#define DEFAULT_COUNT_WIDTH 48
>
>  #define HPCR           "<0, 0x0>"      /* PMU Control reg */
>  #define HPCNTENR       "<0, 0x4>"      /* Count Enable reg */
> @@ -18,6 +19,7 @@ static void (*hw_raw_write_mapping[CSKY_PMU_MAX_EVENTS])(uint64_t val);
>
>  struct csky_pmu_t {
>         struct pmu      pmu;
> +       uint32_t        count_width;
>         uint32_t        hpcr;
>  } csky_pmu;
>
> @@ -806,7 +808,12 @@ static void csky_perf_event_update(struct perf_event *event,
>                                    struct hw_perf_event *hwc)
>  {
>         uint64_t prev_raw_count = local64_read(&hwc->prev_count);
> -       uint64_t new_raw_count = hw_raw_read_mapping[hwc->idx]();
> +       /*
> +        * Sign extend count value to 64bit, otherwise delta calculation
> +        * would be incorrect when overflow occurs.
> +        */
> +       uint64_t new_raw_count = sign_extend64(
> +                       hw_raw_read_mapping[hwc->idx](), csky_pmu.count_width);
csky_pmu.count_width - 1 ? we need index here.

Best Regards
 Guo Ren