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Date:   Wed, 8 Aug 2018 11:33:51 -0500
From:   "Alex G." <mr.nuke.me@...il.com>
To:     Tal Gilboa <talgi@...lanox.com>, Leon Romanovsky <leon@...nel.org>
Cc:     linux-pci@...r.kernel.org, bhelgaas@...gle.com,
        jakub.kicinski@...ronome.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>,
        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 v6 8/9] net/mlx5: Do not call pcie_print_link_status()



On 08/08/2018 10:56 AM, Tal Gilboa wrote:
> On 8/8/2018 6:41 PM, Leon Romanovsky wrote:
>> On Wed, Aug 08, 2018 at 05:23:12PM +0300, Tal Gilboa wrote:
>>> On 8/8/2018 9:08 AM, Leon Romanovsky wrote:
>>>> On Mon, Aug 06, 2018 at 06:25:42PM -0500, Alexandru Gagniuc wrote:
>>>>> This is now done by the PCI core to warn of sub-optimal bandwidth.
>>>>>
>>>>> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
>>>>> ---
>>>>>    drivers/net/ethernet/mellanox/mlx5/core/main.c | 4 ----
>>>>>    1 file changed, 4 deletions(-)
>>>>>
>>>>
>>>> Thanks,
>>>> Reviewed-by: Leon Romanovsky <leonro@...lanox.com>
>>>>
>>>
>>> Alex,
>>> I loaded mlx5 driver with and without these series. The report in 
>>> dmesg is
>>> now missing. From what I understood, the status should be reported at 
>>> least
>>> once, even if everything is in order.
>>
>> It is not what this series is doing and it removes prints completely if
>> fabric can deliver more than card is capable.
>>
>>> We need this functionality to stay.
>>
>> I'm not sure that you need this information in driver's dmesg output,
>> but most probably something globally visible and accessible per-pci
>> device.
> 
> Currently we have users that look for it. If we remove the dmesg print 
> we need this to be reported elsewhere. Adding it to sysfs for example 
> should be a valid solution for our case.

I think a stop-gap measure is to leave the pcie_print_link_status() call 
in drivers that really need it for whatever reason. Implementing a 
reliable reporting through sysfs might take some tinkering, and I don't 
think it's a sufficient reason to block the heart of this series -- 
being able to detect bottlenecks and link downtraining.

Alex

>>
>>>
>>> net-next (dmesg output for 07:00.0):
>>> [270498.625351] mlx5_core 0000:07:00.0: firmware version: 14.22.4020
>>> [270498.632130] mlx5_core 0000:07:00.0: 63.008 Gb/s available PCIe 
>>> bandwidth
>>> (8 GT/s x8 link)
>>> [270499.169533] (0000:07:00.0): E-Switch: Total vports 9, per vport: max
>>> uc(1024) max mc(16384)
>>> [270499.182358] mlx5_core 0000:07:00.0: Port module event: module 0, 
>>> Cable
>>> plugged
>>>
>>> net-next + patches (dmesg output for 07:00.0):
>>> [  331.608472] mlx5_core 0000:07:00.0: firmware version: 14.22.4020
>>> [  332.564938] (0000:07:00.0): E-Switch: Total vports 9, per vport: max
>>> uc(1024) max mc(16384)
>>> [  332.616271] mlx5_core 0000:07:00.0: Port module event: module 0, 
>>> Cable
>>> plugged
>>>
>>>

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