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Date:   Fri, 13 Mar 2020 14:14:16 +0000
From:   Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To:     Robin Murphy <robin.murphy@arm.com>
CC:     Qi Liu <liuqi115@huawei.com>, <will@kernel.org>,
        <mark.rutland@arm.com>, <bhelgaas@google.com>,
        <linux-pci@vger.kernel.org>, <linuxarm@huawei.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC] perf:Add driver for HiSilicon PCIe PMU
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        <49a04327-b58b-3103-f992-97e8838c41df@arm.com>
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On Fri, 13 Mar 2020 13:23:53 +0000
Robin Murphy <robin.murphy@arm.com> wrote:

> On 2020-03-12 12:06 pm, Qi Liu wrote:
> > From: Qi liu <liuqi115@huawei.com>
> > 
> > PCIe PMU Root Complex Integrate End Point(IEP) device is
> > supported to sample bandwidth, latency, buffer occupation,
> > bandwidth utilization etc.
> > Each PMU IEP device monitors multiple root ports, and each
> > IEP is registered as a pmu in /sys/bus/event_source/devices,
> > so users can select the target IEP, and use filter to select
> > root port, function and event.
> > Filtering options are:
> > event:    - select the event.
> > subevent: - select the subevent.
> > port:     - select target root port.
> > func:     - select target EP device under the port.
> > 
> > Example: hisi_pcie_00_14_00/event=0x08,subevent=0x04,   \
> > port=0x05,func=0x00/ -I 1000
> > 
> > PMU IEP device is described by its bus, device and function,
> > target root port is 0x05 and target EP under it is function
> > 0x00. Subevent 0x04 of event 0x08 is sampled.
> > 
> > Note that in this RFC:
> > 1. PCIe PMU IEP hardware is still in development.
> > 2. Perf common event list is undetermined, and name of these
> > events still need to be discussed.
> > 3. port filter could only select one port each time.
> > 4. There are two possible schemes of pmu registration, one is
> > register each root port as a pmu, it is easier for users to
> > select target port. The other one is register each IEP as pmu,
> > for counters are per IEP, not per root port, the second scheme
> > describes hardware PMC much more reasonable, but need to add
> > "port" filter option to select port. We use the second one in
> > this RFC.
> > 

Whilst it's great to have detailed feedback, just to make it clear...

This is an RFC for the reasons above.  They include that the hardware
is still in development - i.e. we can't test it because they've not finished
implementation yet.

The intention of posting so early is to get some feedback on the general
approach and the specific points in 2,3 and 4 above.

The key fiddly point with this is that it is a shared PMU across a set
of PCIe Root Ports (there are several of these devices on each SoC in
the system covering a set of ports each).
That makes for a somewhat fiddly interface, hence the RFC.

Thanks to everyone who has reviewed though as definitely some stuff for liuqi to
fix!

Jonathan