[Intel-wired-lan] [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed and whether it's limited

Mon Apr 2 21:09:02 UTC 2018

On 4/2/2018 11:25 PM, Keller, Jacob E wrote:
> 
> 
>> -----Original Message-----
>> From: Bjorn Helgaas [mailto:helgaas at kernel.org]
>> Sent: Monday, April 02, 2018 12:58 PM
>> To: Keller, Jacob E <jacob.e.keller at intel.com>
>> Cc: Tal Gilboa <talgi at mellanox.com>; Tariq Toukan <tariqt at mellanox.com>; Ariel
>> Elior <ariel.elior at cavium.com>; Ganesh Goudar <ganeshgr at chelsio.com>;
>> Kirsher, Jeffrey T <jeffrey.t.kirsher at intel.com>; everest-linux-l2 at cavium.com;
>> intel-wired-lan at lists.osuosl.org; netdev at vger.kernel.org; linux-
>> kernel at vger.kernel.org; linux-pci at vger.kernel.org
>> Subject: Re: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed
>> and whether it's limited
>>
>> On Mon, Apr 02, 2018 at 04:25:17PM +0000, Keller, Jacob E wrote:
>>>> -----Original Message-----
>>>> From: Bjorn Helgaas [mailto:helgaas at kernel.org]
>>>> Sent: Friday, March 30, 2018 2:05 PM
>>>> To: Tal Gilboa <talgi at mellanox.com>
>>>> Cc: Tariq Toukan <tariqt at mellanox.com>; Keller, Jacob E
>>>> <jacob.e.keller at intel.com>; Ariel Elior <ariel.elior at cavium.com>; Ganesh
>>>> Goudar <ganeshgr at chelsio.com>; Kirsher, Jeffrey T
>>>> <jeffrey.t.kirsher at intel.com>; everest-linux-l2 at cavium.com; intel-wired-
>>>> lan at lists.osuosl.org; netdev at vger.kernel.org; linux-kernel at vger.kernel.org;
>>>> linux-pci at vger.kernel.org
>>>> Subject: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed
>> and
>>>> whether it's limited
>>>>
>>>> From: Tal Gilboa <talgi at mellanox.com>
>>>>
>>>> Add pcie_print_link_status().  This logs the current settings of the link
>>>> (speed, width, and total available bandwidth).
>>>>
>>>> If the device is capable of more bandwidth but is limited by a slower
>>>> upstream link, we include information about the link that limits the
>>>> device's performance.
>>>>
>>>> The user may be able to move the device to a different slot for better
>>>> performance.
>>>>
>>>> This provides a unified method for all PCI devices to report status and
>>>> issues, instead of each device reporting in a different way, using
>>>> different code.
>>>>
>>>> Signed-off-by: Tal Gilboa <talgi at mellanox.com>
>>>> [bhelgaas: changelog, reword log messages, print device capabilities when
>>>> not limited]
>>>> Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
>>>> ---
>>>>   drivers/pci/pci.c   |   29 +++++++++++++++++++++++++++++
>>>>   include/linux/pci.h |    1 +
>>>>   2 files changed, 30 insertions(+)
>>>>
>>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>>> index e00d56b12747..cec7aed09f6b 100644
>>>> --- a/drivers/pci/pci.c
>>>> +++ b/drivers/pci/pci.c
>>>> @@ -5283,6 +5283,35 @@ u32 pcie_bandwidth_capable(struct pci_dev *dev,
>>>> enum pci_bus_speed *speed,
>>>>   	return *width * PCIE_SPEED2MBS_ENC(*speed);
>>>>   }
>>>>
>>>> +/**
>>>> + * pcie_print_link_status - Report the PCI device's link speed and width
>>>> + * @dev: PCI device to query
>>>> + *
>>>> + * Report the available bandwidth at the device.  If this is less than the
>>>> + * device is capable of, report the device's maximum possible bandwidth and
>>>> + * the upstream link that limits its performance to less than that.
>>>> + */
>>>> +void pcie_print_link_status(struct pci_dev *dev)
>>>> +{
>>>> +	enum pcie_link_width width, width_cap;
>>>> +	enum pci_bus_speed speed, speed_cap;
>>>> +	struct pci_dev *limiting_dev = NULL;
>>>> +	u32 bw_avail, bw_cap;
>>>> +
>>>> +	bw_cap = pcie_bandwidth_capable(dev, &speed_cap, &width_cap);
>>>> +	bw_avail = pcie_bandwidth_available(dev, &limiting_dev, &speed,
>>>> &width);
>>>> +
>>>> +	if (bw_avail >= bw_cap)
>>>> +		pci_info(dev, "%d Mb/s available bandwidth (%s x%d link)\n",
>>>> +			 bw_cap, PCIE_SPEED2STR(speed_cap), width_cap);
>>>> +	else
>>>> +		pci_info(dev, "%d Mb/s available bandwidth, limited by %s x%d
>>>> link at %s (capable of %d Mb/s with %s x%d link)\n",
>>>> +			 bw_avail, PCIE_SPEED2STR(speed), width,
>>>> +			 limiting_dev ? pci_name(limiting_dev) : "<unknown>",
>>>> +			 bw_cap, PCIE_SPEED2STR(speed_cap), width_cap);
>>>> +}
>>>
>>> Personally, I would make thic last one a pci_warn() to indicate it at a
>>> higher log level, but I'm  ok with the wording, and if consensus is that
>>> this should be at info, I'm ok with that.
>>
>> Tal's original patch did have a pci_warn() here, and we went back and
>> forth a bit.  They get bug reports when a device doesn't perform as
>> expected, which argues for pci_warn().  But they also got feedback
>> saying warnings are a bit too much, which argues for pci_info() [1]
>>
>> I don't have a really strong opinion either way.  I have a slight
>> preference for info because the user may not be able to do anything
>> about it (there may not be a faster slot available), and I think
>> distros are usually configured so a warning interrupts the smooth
>> graphical boot.
>>
>> It looks like mlx4, fm10k, and ixgbe currently use warnings, while
>> bnx2x, bnxt_en, and cxgb4 use info.  It's a tie so far :)
>>
>> [1] https://lkml.kernel.org/r/e47f3628-b56c-4d0a-f18b-
>> 5ffaf261ccc0 at mellanox.com
>>
> 
> With that information, I'm fine with the proposal to display this as only an info. The message is still printed and can be used for debugging purposes, and I think that's really enough.
> 
>> Here's a proposal for printing the bandwidth as "x.xxx Gb/s":
> 
> Nice, I like that also.
> 
> Regards,
> Jake
> 

Same here for both.