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

[John Garry]

On 26/06/2021 03:13, liuqi (BA) wrote:
> On 2021/6/25 23:53, John Garry wrote:
> > On 24/06/2021 11:59, Qi Liu wrote:
> > > +
> > > +/*
> > > + * Events with the "dl" suffix in their names count performance in 
> > > DL layer,
> > > + * otherswise, events count performance in TL layer.
> > > + */
> > > +static struct attribute *hisi_pcie_pmu_events_attr[] = {
> > > +    HISI_PCIE_PMU_EVENT_ATTR(bw_rx_mwr, 0x010004),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(bw_rx_mrd, 0x100005),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(bw_tx_mwr, 0x010005),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(bw_tx_mrd, 0x200004),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(lat_rx_mwr, 0x000010),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(lat_rx_mrd, 0x020010),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(lat_tx_mrd, 0x000011),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(bw_rx_dl, 0x010084),
> > > +    HISI_PCIE_PMU_EVENT_ATTR(bw_tx_dl, 0x030084),
> > > +    NULL
> > > +};
> > > +
> > > +static struct attribute_group hisi_pcie_pmu_events_group = {
> > > +    .name = "events",
> > > +    .attrs = hisi_pcie_pmu_events_attr,
> > > +};
> > > +
> > > +static struct attribute *hisi_pcie_pmu_format_attr[] = {
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(event, "config:0-15"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(subevent, "config:16-23"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(thr_len, "config1:0-3"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(thr_mode, "config1:4"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(trig_len, "config1:5-8"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(trig_mode, "config1:9"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(port, "config2:0-15"),
> > > +    HISI_PCIE_PMU_FORMAT_ATTR(bdf, "config2:16-31"),
> > > +    NULL
> > > +};
> >
> > I am just wondering how this now works.
> >
> > So if the user programs the following:
> > ./perf stat -v -e hisi_pcieX/lat_rx_mrd/
> >
> > Then the value (incremented) in HISI_PCIE_CNT (I think that's the 
> > right one) is returned as the event count. But one would expect 
> > bandwidth from that event, while we only return here the delay cycles 
> > - how is the count in HISI_PCIE_CNT_EXT exposed, so userspace can do 
> > the calc for bw?

Hi Qi,

> 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/

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@event\\=0x4@subevent\\=0x02 \ 
hisi_pcieX@event\\=0x1000@subevent\\=0x02 \",
   "Unit": "hisi_pci",
   "Compat": "v1"
},

(syntax may be incorrect - illustration only)

> 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.

Thanks,
John