linux-kernel - Re: [PATCH] PCI/LINK: Account for BW notification in vector calculation

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Date:   Mon, 22 Apr 2019 18:33:47 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Alex G <mr.nuke.me@...il.com>
Cc:     bhelgaas@...gle.com, helgaas@...nel.org, linux-pci@...r.kernel.org,
        austin_bolen@...l.com, alex_gagniuc@...lteam.com,
        keith.busch@...el.com, Shyam_Iyer@...l.com, lukas@...ner.de,
        okaya@...nel.org, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/LINK: Account for BW notification in vector
 calculation

On Mon, 22 Apr 2019 19:05:57 -0500
Alex G <mr.nuke.me@...il.com> wrote:

> On 4/22/19 5:43 PM, Alex Williamson wrote:
> > [  329.725607] vfio-pci 0000:07:00.0: 32.000 Gb/s available PCIe bandwidth,
> > limited by 2.5 GT/s x16 link at 0000:00:02.0 (capable of 64.000 Gb/s with 5
> > GT/s x16 link)
> > [  708.151488] vfio-pci 0000:07:00.0: 32.000 Gb/s available PCIe bandwidth,
> > limited by 2.5 GT/s x16 link at 0000:00:02.0 (capable of 64.000 Gb/s with 5
> > GT/s x16 link)
> > [  718.262959] vfio-pci 0000:07:00.0: 32.000 Gb/s available PCIe bandwidth,
> > limited by 2.5 GT/s x16 link at 0000:00:02.0 (capable of 64.000 Gb/s with 5
> > GT/s x16 link)
> > [ 1138.124932] vfio-pci 0000:07:00.0: 32.000 Gb/s available PCIe bandwidth,
> > limited by 2.5 GT/s x16 link at 0000:00:02.0 (capable of 64.000 Gb/s with 5
> > GT/s x16 link)
> > 
> > What is the value of this nagging?  
> 
> Good! The bandwidth notification service is working as intended. If this 
> bothers you, you can unbind the device from the bandwidth notification 
> driver:
> 
> echo 0000:07:00.0:pcie010 |
> sudo tee /sys/bus/pci_express/drivers/pcie_bw_notification/unbind

That's a bad solution for users, this is meaningless tracking of a
device whose driver is actively managing the link bandwidth for power
purposes.  There is nothing wrong happening here that needs to fill
logs.  I thought maybe if I enabled notification of autonomous
bandwidth changes that it might categorize these as something we could
ignore, but it doesn't.  How can we identify only cases where this is
an erroneous/noteworthy situation?  Thanks,

Alex

> > diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
> > index 7d04f9d087a6..1b330129089f 100644
> > --- a/drivers/pci/pcie/portdrv_core.c
> > +++ b/drivers/pci/pcie/portdrv_core.c
> > @@ -55,7 +55,8 @@ static int pcie_message_numbers(struct pci_dev *dev, int mask,
> >   	 * 7.8.2, 7.10.10, 7.31.2.
> >   	 */
> >   
> > -	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP)) {
> > +	if (mask & (PCIE_PORT_SERVICE_PME | PCIE_PORT_SERVICE_HP |
> > +		    PCIE_PORT_SERVICE_BWNOTIF)) {
> >   		pcie_capability_read_word(dev, PCI_EXP_FLAGS, &reg16);
> >   		*pme = (reg16 & PCI_EXP_FLAGS_IRQ) >> 9;
> >   		nvec = *pme + 1;  
> 
> Good catch!