Re: [PATCH RESEND 0/4] Add support for HiSilicon PCIe Tune and Trace device
From: Suzuki K Poulose
Date: Mon Apr 19 2021 - 07:17:50 EST
On 17/04/2021 11:17, Yicong Yang wrote:
[RESEND with perf and coresight folks Cc'ed]
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).
PTT tune is designed for monitoring and adjusting PCIe link parameters.
We provide several parameters of the PCIe link. Through the driver,
user can adjust the value of certain parameter to affect the PCIe link
for the purpose of enhancing the performance in certian situation.
...
The reason for not using perf is because there is no current support
for uncore tracing in the perf facilities. We have our own format
of data and don't need perf doing the parsing. The setting through
perf tools doesn't seem to be friendly as well. For example,
we cannot count on perf to decode the usual format BDF number like
<domain>:<bus>:<dev>.<fn>, which user can use to filter the TLP
headers through the PTT device.
A similar approach for implementing this function is ETM, which use
sysfs for configuring and a character device for dumping data.
Greg has some comments on our implementation and doesn't advocate
to build driver on debugfs [1]. So I resend this series to
collect more feedbacks on the implementation of this driver.
Hi perf and ETM related experts, is it suggested to adapt this driver
to perf? Or is the debugfs approach acceptable? Otherwise use
sysfs + character device like ETM and use perf tools for decoding it?
Any comments is welcomed.
Please use perf. Debugfs / sysfs is not the right place for these things.
Also, please move your driver to drivers/perf/
As Alex mentioned, the ETM drivers were initially developed when the AUX
buffer was not available. The sysfs interface is there only for the
backward compatibility and for bring up ( due to the nature of the
connections between the CoreSight components and sometimes the missing
engineering spec).
Suzuki