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

[John Garry]

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@event\\=0x4@subevent\\=0x02 \
> > hisi_pcieX@event\\=0x1000@subevent\\=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@event\\=0x4\\,subevent\\=0x2@ / 
hisi_pcieX@event\\=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