linux-kernel - Re: [PATCH v7 2/2] drivers/perf: hisi: Add driver for HiSilicon PCIe PMU

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Date:   Mon, 28 Jun 2021 13:11:33 +0100
From:   John Garry <john.garry@...wei.com>
To:     "liuqi (BA)" <liuqi115@...wei.com>, Linuxarm <linuxarm@...wei.com>,
        "will@...nel.org" <will@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Zhangshaokun <zhangshaokun@...ilicon.com>
Subject: Re: [PATCH v7 2/2] drivers/perf: hisi: Add driver for HiSilicon PCIe
 PMU

On 28/06/2021 11:49, liuqi (BA) wrote:
>>> Hardware counter and ext_counter work together for bandwidth, latency,
>>> bus utilization and buffer occupancy events. For example, for latency
>>> events(idx = 0x10), counter counts total delay cycles and ext_counter
>>> counts PCIe packets number.
>>>
>>> As we don't want PMU driver to process these two data, "delay cycles"
>>> can be treated as an event(id = 0x10), "packets number" as another event
>>> (id = 0x10 << 8), and driver could export these data separately.
>>>
>>> if the user want to calculate latency of rx memory read, they should:
>>> ./perf stat -v -e '{hisi_pcieX/event=0x10,
>>> subevent=0x01/,hisi_pcieX/event=0x0400, subevent=0x01/
>>>
>>> and for bandwidth event:
>>> ./perf stat -v -e '{hisi_pcieX/event=0x4,
>>> subevent=0x02/,hisi_pcieX/event=0x1000, subevent=0x02/
> Hi John,
>> I would suggest supporting a perf metric for this then, which would be
>> like:
>>
>> {
>>      "BriefDescription": "Latency for inbound traffic...",
>>      "MetricName": "hisi_pcie_lat_rx_mrd",
>>      "MetricExpr": "hisi_pcieX@...nt\\=0x4@...event\\=0x02 \
>> hisi_pcieX@...nt\\=0x1000@...event\\=0x02 \",
>>      "Unit": "hisi_pci",
>>      "Compat": "v1"
>> },
>>
>> (syntax may be incorrect - illustration only)
>>
> yes, we could add these metrics in json file, thanks.

The syntax is actually like:
    "MetricExpr": "hisi_pcieX@...nt\\=0x4\\,subevent\\=0x2@ / 
hisi_pcieX@...nt\\=0x1000\\,subevent\\=0x2@",

>>> Then the value in HISI_PCIE_CNT and HISI_PCIE_EXT_CNT returned
>>> separately, and userspace could do the calculation.
>> But I am still curious about lat_rx_mrd and the other events which we
>> continue to advertise. They don't really provide latency or bandwidth on
>> their own, but only half the necessary data. So I doubt their purpose.
>>
> So how about changing the event name to show the real purpose of this
> event, like changing "bw_rx_mrd" to "flux_rx_mrd", and changing
> "lat_rx_mrd" to "delay_rx_mrd"?

eh, I suppose you could, but I am not sure of the value. However I 
assume that the driver will detect and reject invalid or nonsense 
combinations of events if you did want this.

Thanks,
John