linux-kernel - Re: [PATCH 0/4] Add support for HiSilicon PCIe Tune and Trace device

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Date:   Thu, 8 Apr 2021 21:25:56 +0800
From:   Yicong Yang <yangyicong@...ilicon.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <alexander.shishkin@...ux.intel.com>, <helgaas@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <lorenzo.pieralisi@....com>, <jonathan.cameron@...wei.com>,
        <song.bao.hua@...ilicon.com>, <prime.zeng@...wei.com>,
        <linux-doc@...r.kernel.org>, <linuxarm@...wei.com>,
        "liuqi (BA)" <liuqi115@...wei.com>
Subject: Re: [PATCH 0/4] Add support for HiSilicon PCIe Tune and Trace device

On 2021/4/7 18:25, Greg KH wrote:
> On Wed, Apr 07, 2021 at 06:03:11PM +0800, Yicong Yang wrote:
>> On 2021/4/6 21:49, Greg KH wrote:
>>> On Tue, Apr 06, 2021 at 08:45:50PM +0800, Yicong Yang wrote:
>>>> HiSilicon PCIe tune and trace device(PTT) is a PCIe Root Complex
>>>> integrated Endpoint(RCiEP) device, providing the capability
>>>> to dynamically monitor and tune the PCIe traffic(tune),
>>>> and trace the TLP headers(trace). The driver exposes the user
>>>> interface through debugfs, so no need for extra user space tools.
>>>> The usage is described in the document.
>>>
>>> Why use debugfs and not the existing perf tools for debugging?
>>>
>>
>> The perf doesn't match our device as we've analyzed.
>>
>> For the tune function it doesn't do the sampling at all.
>> User specifys one link parameter and reads its current value or set
>> the desired one. The process is static. We didn't find a
>> way to adapt to perf.
>>
>> For the trace function, we may barely adapt to the perf framework
>> but it doesn't seems like a better choice. We have our own format
>> of data and don't need perf doing the parsing, and we'll get extra
>> information added by perf as well. The settings through perf tools
>> won't satisfy our needs, we cannot present available settings
>> (filter BDF number, TLP types, buffer controls) to
>> the user and user cannot set in a friendly way. For example,
>> we cannot count on perf to decode the usual format BDF number like
>> <domain>:<bus>:<dev>.<fn>, which user can use filter the TLP
>> headers.
> 
> Please work with the perf developers to come up with a solution.  I find
> it hard to believe that your hardware is so different than all the other
> hardware that perf currently supports.  I would need their agreement
> that you can not use perf before accepting this patchset.
> 

Sure. I'll resend this series with more detailed information and with perf list
and developers cc'ed to collect more suggestions on this device and driver.

Thanks,
Yicong