netdev - Re: [PATCH v3 net-next 5/8] net/ncsi: Dump NCSI packet statistics

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Message-Id: <20170420233812.GA7223@gwshan>
Date:   Fri, 21 Apr 2017 09:38:12 +1000
From:   Gavin Shan <gwshan@...ux.vnet.ibm.com>
To:     David Miller <davem@...emloft.net>
Cc:     gwshan@...ux.vnet.ibm.com, netdev@...r.kernel.org, joe@...ches.com,
        kubakici@...pl
Subject: Re: [PATCH v3 net-next 5/8] net/ncsi: Dump NCSI packet statistics

On Thu, Apr 20, 2017 at 01:21:03PM -0400, David Miller wrote:
>From: Gavin Shan <gwshan@...ux.vnet.ibm.com>
>Date: Tue, 18 Apr 2017 16:51:32 +1000
>
>> This creates /sys/kernel/debug/ncsi/<eth0>/stats to dump the NCSI
>> packets sent and received over all packages and channels. It's useful
>> to diagnose NCSI problems, especially when NCSI packages and channels
>> aren't probed properly. The statistics can be gained from debugfs file
>> as below:
>> 
>>  # cat /sys/kernel/debug/ncsi/eth0/stats
>
>There is no reason you cannot use ethtool statistics to provide this
>information to the user.
>

It can be dumped by ethtool, but it's more reasonable to dump them
through debugfs for couple of reasons: (1) ethtool usually dumps
statistics collected by hardware, but this debugfs file dumps the
statistics of packets seen (collected) by software. They are different
things. Note that NCSI channel collects statistics in hardware and it's
not exposed or dumped by this patchset. They are candidates for ethtool.
(2) To expose this through ethtool relies on the availability of the tool.
It's nicer not to depend on it. (3) This interface can be used to check
the debug packet has been sent successfully through /sys/kernel/debug/ncsi/eth0/pkt,
dumping the statistics through debugfs make this (debugging) mechanism
consistent.

Thanks,
Gavin