linux-kernel - Re: [PATCH 1/9] PCI: sysfs: Export available PCIe bandwidth

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Date:   Wed, 5 Sep 2018 08:52:31 -0500
From:   "Alex G." <mr.nuke.me@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     linux-pci@...r.kernel.org, bhelgaas@...gle.com,
        keith.busch@...el.com, alex_gagniuc@...lteam.com,
        austin_bolen@...l.com, shyam_iyer@...l.com,
        Ariel Elior <ariel.elior@...ium.com>,
        everest-linux-l2@...ium.com,
        "David S. Miller" <davem@...emloft.net>,
        Michael Chan <michael.chan@...adcom.com>,
        Ganesh Goudar <ganeshgr@...lsio.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Dirk van der Merwe <dirk.vandermerwe@...ronome.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, linux-rdma@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [PATCH 1/9] PCI: sysfs: Export available PCIe bandwidth

On 09/05/2018 02:26 AM, Stephen Hemminger wrote:
> On Mon,  3 Sep 2018 13:02:28 -0500
> Alexandru Gagniuc <mr.nuke.me@...il.com> wrote:
> 
>> For certain bandwidth-critical devices (e.g. multi-port network cards)
>> it is useful to know the available bandwidth to the root complex. This
>> information is only available via the system log, which doesn't
>> account for link degradation after probing.
>>
>> With a sysfs attribute, we can computes the bandwidth on-demand, and
>> will detect degraded links.
>>
>> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
> 
> In other places (like /sys/class/net/eth0/speed) only the raw value is printed
> without suffix.  The general convention in sysfs is that it should be one value
> per file and in more raw format.  So why not just print it in bits/sec without
> suffix?

I wanted to be consistent with other PCIe exports that use units.For 
example:

/sys/devices/pci0000:3a/0000:3a:00.0/0000:3b:00.0/0000:3c:05.0/max_link_speed:8 
GT/s
/sys/devices/pci0000:3a/0000:3a:00.0/0000:3b:00.0/0000:3c:05.0/current_link_speed:2.5 
GT/s
/sys/bus/pci/slots/182/cur_bus_speed:2.5 GT/s PCIe
/sys/bus/pci/slots/182/max_bus_speed:8.0 GT/s PCIe