linux-kernel - Re: [RESEND PATCH V7 2/2] drivers/perf: hisi: add driver for HNS3 PMU

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Message-ID: <20220627105211.GD22095@willie-the-truck>
Date:   Mon, 27 Jun 2022 11:52:12 +0100
From:   Will Deacon <will@...nel.org>
To:     Guangbin Huang <huangguangbin2@...wei.com>
Cc:     john.garry@...wei.com, mark.rutland@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, liuqi115@...wei.com,
        zhangshaokun@...ilicon.com, f.fangjian@...wei.com,
        lipeng321@...wei.com, shenjian15@...wei.com
Subject: Re: [RESEND PATCH V7 2/2] drivers/perf: hisi: add driver for HNS3 PMU

On Wed, May 25, 2022 at 08:52:11AM +0800, Guangbin Huang wrote:
> HNS3(HiSilicon Network System 3) PMU is RCiEP device in HiSilicon SoC NIC,
> supports collection of performance statistics such as bandwidth, latency,
> packet rate and interrupt rate.
> 
> NIC of each SICL has one PMU device for it. Driver registers each PMU
> device to perf, and exports information of supported events, filter mode of
> each event, bdf range, hardware clock frequency, identifier and so on via
> sysfs.
> 
> Each PMU device has its own registers of control, counters and interrupt,
> and it supports 8 hardware events, each hardward event has its own
> registers for configuration, counters and interrupt.
> 
> Filter options contains:
> event        - select event
> port         - select physical port of nic
> tc           - select tc(must be used with port)
> func         - select PF/VF
> queue        - select queue of PF/VF(must be used with func)
> intr         - select interrupt number(must be used with func)
> global       - select all functions of IO DIE
> 
> Signed-off-by: Guangbin Huang <huangguangbin2@...wei.com>
> Reviewed-by: John Garry <john.garry@...wei.com>
> Reviewed-by: Shaokun Zhang <zhangshaokun@...ilicon.com>
> ---
>  MAINTAINERS                       |    6 +
>  drivers/perf/hisilicon/Kconfig    |   10 +
>  drivers/perf/hisilicon/Makefile   |    1 +
>  drivers/perf/hisilicon/hns3_pmu.c | 1662 +++++++++++++++++++++++++++++
>  include/linux/cpuhotplug.h        |    1 +
>  5 files changed, 1680 insertions(+)
>  create mode 100644 drivers/perf/hisilicon/hns3_pmu.c

This mostly looks good to me, but I have one niggling concern with the ABI:

> +#define HNS3_PMU_FILTER_ATTR(_name, _config, _start, _end)               \
> +	static inline u64 hns3_pmu_get_##_name(struct perf_event *event) \
> +	{                                                                \
> +		return FIELD_GET(GENMASK_ULL(_end, _start),              \
> +				 event->attr._config);                   \
> +	}
> +
> +HNS3_PMU_FILTER_ATTR(event, config, 0, 16);
> +HNS3_PMU_FILTER_ATTR(subevent, config, 0, 7);
> +HNS3_PMU_FILTER_ATTR(event_type, config, 8, 15);
> +HNS3_PMU_FILTER_ATTR(ext_counter_used, config, 16, 16);
> +HNS3_PMU_FILTER_ATTR(real_event, config, 0, 15);

How does perf tool deal with overlapping fields like this? It seems like
quite a bad idea to allow things like "event=0xffff,subevent=0" when they
are no longer distinct and I don't _think_ any other drivers do this.

Can you remove 'event' and 'real_event' for now, or are they needed?

Will