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

From: Greg KH <gregkh@linuxfoundation.org>
To: Yicong Yang <yangyicong@hisilicon.com>
Cc: alexander.shishkin@linux.intel.com, helgaas@kernel.org,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	lorenzo.pieralisi@arm.com, jonathan.cameron@huawei.com,
	song.bao.hua@hisilicon.com, prime.zeng@huawei.com,
	linux-doc@vger.kernel.org, linuxarm@huawei.com,
	"liuqi (BA)" <liuqi115@huawei.com>
Subject: Re: [PATCH 0/4] Add support for HiSilicon PCIe Tune and Trace device
Date: Wed, 7 Apr 2021 12:25:29 +0200	[thread overview]
Message-ID: <YG2Imet/tbyzYcOo@kroah.com> (raw)
In-Reply-To: <01b6e8f7-3282-514e-818d-0e768dcc5ba3@hisilicon.com>

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.

thanks,

greg k-h