linux-kernel - Re: [PATCH v3 3/3] perf: xgene: Add support for SoC PMU version 3

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Message-ID: <CAFHUOYyjXOMRCOg7wSZ3VNC2XcxXUHE3HPayOykjftPecn1ftA@mail.gmail.com>
Date:   Thu, 22 Jun 2017 11:28:27 -0700
From:   Hoan Tran <hotran@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Will Deacon <will.deacon@....com>,
        lkml <linux-kernel@...r.kernel.org>, Loc Ho <lho@....com>,
        linux-arm-kernel@...ts.infradead.org, Tai Nguyen <ttnguyen@....com>
Subject: Re: [PATCH v3 3/3] perf: xgene: Add support for SoC PMU version 3

Hi Mark,

On Thu, Jun 22, 2017 at 11:18 AM, Mark Rutland <mark.rutland@....com> wrote:
> On Thu, Jun 22, 2017 at 06:52:56PM +0100, Mark Rutland wrote:
>> Hi Hoan,
>>
>> This largely looks good; I have one minor comment.
>>
>> On Tue, Jun 06, 2017 at 11:02:26AM -0700, Hoan Tran wrote:
>> >  static inline void
>> > +xgene_pmu_write_counter64(struct xgene_pmu_dev *pmu_dev, int idx, u64 val)
>> > +{
>> > +   u32 cnt_lo, cnt_hi;
>> > +
>> > +   cnt_hi = upper_32_bits(val);
>> > +   cnt_lo = lower_32_bits(val);
>> > +
>> > +   /* v3 has 64-bit counter registers composed by 2 32-bit registers */
>> > +   xgene_pmu_write_counter32(pmu_dev, 2 * idx, cnt_lo);
>> > +   xgene_pmu_write_counter32(pmu_dev, 2 * idx + 1, cnt_hi);
>> > +}
>>
>> For this to be atomic, we need to disable the counters for the duration
>> of the IRQ handler, which we don't do today.
>>
>> Regardless, we should do that to ensure that groups are self-consistent.
>>
>> i.e. in xgene_pmu_isr() we should call ops->stop_counters() just after
>> taking the pmu lock, and we should call ops->start_counters() just
>> before releasing it.
>>
>> With that:
>>
>> Acked-by: Mark Rutland <mark.rutland@....com>
>
> Actually, that should be in _xgene_pmu_isr, given we have to do it for each
> pmu_dev.
>
> I'll apply the diff below; this also avoids a race on V1 where an
> overflow could be lost (as we clear the whole OVSR rather than only the
> set bits).

Yes, I'm good about that. Thanks

Regards
Hoan

>
> Thanks,
> Mark.
>
> diff --git a/drivers/perf/xgene_pmu.c b/drivers/perf/xgene_pmu.c
> index 84c32e0..a9659cb 100644
> --- a/drivers/perf/xgene_pmu.c
> +++ b/drivers/perf/xgene_pmu.c
> @@ -1217,13 +1217,15 @@ static void _xgene_pmu_isr(int irq, struct xgene_pmu_dev *pmu_dev)
>         u32 pmovsr;
>         int idx;
>
> +       xgene_pmu->ops->stop_counters(pmu_dev);
> +
>         if (xgene_pmu->version == PCP_PMU_V3)
>                 pmovsr = readl(csr + PMU_PMOVSSET) & PMU_OVERFLOW_MASK;
>         else
>                 pmovsr = readl(csr + PMU_PMOVSR) & PMU_OVERFLOW_MASK;
>
>         if (!pmovsr)
> -               return;
> +               goto out;
>
>         /* Clear interrupt flag */
>         if (xgene_pmu->version == PCP_PMU_V1)
> @@ -1243,6 +1245,9 @@ static void _xgene_pmu_isr(int irq, struct xgene_pmu_dev *pmu_dev)
>                 xgene_perf_event_update(event);
>                 xgene_perf_event_set_period(event);
>         }
> +
> +out:
> +       xgene_pmu->ops->start_counters(pmu_dev);
>  }
>
>  static irqreturn_t xgene_pmu_isr(int irq, void *dev_id)
>