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

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Message-ID: <02874ECE860811409154E81DA85FBB5882D7BF4B@ORSMSX115.amr.corp.intel.com>
Date:   Fri, 13 Apr 2018 15:34:08 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>, Jakub Kicinski <kubakici@...pl>
CC:     Tal Gilboa <talgi@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Ariel Elior <ariel.elior@...ium.com>,
        Ganesh Goudar <ganeshgr@...lsio.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "everest-linux-l2@...ium.com" <everest-linux-l2@...ium.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link
 speed and whether it's limited



> -----Original Message-----
> From: Bjorn Helgaas [mailto:helgaas@...nel.org]
> Sent: Friday, April 13, 2018 7:07 AM
> To: Jakub Kicinski <kubakici@...pl>
> Cc: Tal Gilboa <talgi@...lanox.com>; Tariq Toukan <tariqt@...lanox.com>;
> Keller, Jacob E <jacob.e.keller@...el.com>; Ariel Elior <ariel.elior@...ium.com>;
> Ganesh Goudar <ganeshgr@...lsio.com>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher@...el.com>; everest-linux-l2@...ium.com; intel-wired-
> lan@...ts.osuosl.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-pci@...r.kernel.org
> Subject: Re: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed
> and whether it's limited
> 
> On Thu, Apr 12, 2018 at 09:32:49PM -0700, Jakub Kicinski wrote:
> > On Fri, 30 Mar 2018 16:05:18 -0500, Bjorn Helgaas wrote:
> > > +	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);
> >
> > I was just looking at using this new function to print PCIe BW for a
> > NIC, but I'm slightly worried that there is nothing in the message that
> > says PCIe...  For a NIC some people may interpret the bandwidth as NIC
> > bandwidth:
> >
> > [   39.839989] nfp 0000:04:00.0: Netronome Flow Processor NFP4000/NFP6000
> PCIe Card Probe
> > [   39.848943] nfp 0000:04:00.0: 63.008 Gb/s available bandwidth (8 GT/s x8 link)
> > [   39.857146] nfp 0000:04:00.0: RESERVED BARs: 0.0: General/MSI-X SRAM, 0.1:
> PCIe XPB/MSI-X PBA, 0.4: Explicit0, 0.5: Explicit1, fre4
> >
> > It's not a 63Gbps NIC...  I'm sorry if this was discussed before and I
> > didn't find it.  Would it make sense to add the "PCIe: " prefix to the
> > message like bnx2x used to do?  Like:
> >
> > nfp 0000:04:00.0: PCIe: 63.008 Gb/s available bandwidth (8 GT/s x8 link)
> 
> I agree, that does look potentially confusing.  How about this:
> 
>   nfp 0000:04:00.0: 63.008 Gb/s available PCIe bandwidth (8 GT/s x8 link)
> 
> I did have to look twice at this before I remembered that we're
> printing Gb/s (not GB/s).  Most of the references I found on the web
> use GB/s when talking about total PCIe bandwidth.
> 
> But either way I think it's definitely worth mentioning PCIe
> explicitly.

I also agree printing PCIe explicitly is good.

Thanks,
Jake