linux-kernel - Re: [PATCH] PCI: Reduce verbosity of device enable messages

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Message-ID: <CAFbbpazQU6S4MDAGcHDKG79T2GOaxz9Ezg2Ls6hhPDCTVLrdEA@mail.gmail.com>
Date: Wed, 9 Jul 2025 11:25:54 -0700
From: Ammar Qadri <ammarq@...gle.com>
To: Manivannan Sadhasivam <mani@...nel.org>, Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Reduce verbosity of device enable messages

This is the only message I can see being consistently printed as a
result of the open/close of the devices.

I am not opposed to carrying this out of tree at all, but for the sake
of exhausting options people would be comfortable with, would you
be okay with moving this to dev_dbg, or would you have the same
hesitations, Mani (et al)? Or is there some alternative flag-controlled
behavior you'd recommend?



On Fri, Jun 13, 2025 at 3:09 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Fri, Jun 13, 2025 at 02:40:40PM -0700, Ammar Qadri wrote:
> > Hi Mani,
> >
> > The issue we are experiencing is not caused from
> > removing/reattaching the device driver, so the other messages have
> > not been problematic.
> >
> > The vfio-pci driver is attached to each VF once. Clients in our
> > system call open and close on the vfio-pci driver, respectively, at
> > the start and end of their use, with fairly short-term tenancy,
> > which ends up triggering these enable messages.  This message is
> > proving challenging not only because they are not particularly
> > useful,  but because they are causing log files to rotate once every
> > 30 minutes or so, and we lose a lot of other more valuable logging
> > as a consequence.  I'm open to other solutions, but in my opinion
> > this preserves the message, without over-engineering and introducing
> > throttling or other behaviour.
>
> Are there any other messages associated with the open/close?  I assume
> probably not, or you would want to demote those as well.
>
> I did happen to find some value in this particular message just the
> other day because it showed that a config read was successful after
> previous ones had failed.
>
> But I agree in general that it's fairly low value and at least the
> uninterpreted "%04x -> %04x" part is not really user-friendly.
>
> If people think there's enough value in retaining it at KERN_INFO, I
> suppose there's always the option of carrying an out-of-tree patch to
> demote it?
>
> > On Thu, Jun 12, 2025 at 11:12 PM Manivannan Sadhasivam <mani@...nel.org> wrote:
> > >
> > > On Wed, May 07, 2025 at 11:29:19PM +0000, Ammar Qadri wrote:
> > > > Excessive logging of PCIe device enable operations can create significant
> > > > noise in system logs, especially in environments with a high number of
> > > > such devices, especially VFs.
> > > >
> > > > High-rate logging can cause log files to rotate too quickly, losing
> > > > valuable information from other system components.This commit addresses
> > > > this issue by downgrading the logging level of "enabling device" messages
> > > > from `info` to `dbg`.
> > > >
> > >
> > > While I generally prefer reduced verbosity of the device drivers, demoting an
> > > existing log to debug might surprise users. Especially in this case, the message
> > > is widely used to identify the enablement of a PCI device. So I don't think it
> > > is a good idea to demote it to a debug log.
> > >
> > > But I'm surprised that this single message is creating much overhead in the
> > > logging. I understand that you might have 100s of VFs in cloud environments, but
> > > when a VF is added, a bunch of other messages would also get printed (resource,
> > > IRQ, device driver etc...). Or you considered that this message is not that
> > > important compared to the rest?
> > >
> > > - Mani
> > >
> > > > Signed-off-by: Ammar Qadri <ammarq@...gle.com>
> > > > ---
> > > >  drivers/pci/setup-res.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> > > > index c6657cdd06f67..be669ff6ca240 100644
> > > > --- a/drivers/pci/setup-res.c
> > > > +++ b/drivers/pci/setup-res.c
> > > > @@ -516,7 +516,7 @@ int pci_enable_resources(struct pci_dev *dev, int mask)
> > > >       }
> > > >
> > > >       if (cmd != old_cmd) {
> > > > -             pci_info(dev, "enabling device (%04x -> %04x)\n", old_cmd, cmd);
> > > > +             pci_dbg(dev, "enabling device (%04x -> %04x)\n", old_cmd, cmd);
> > > >               pci_write_config_word(dev, PCI_COMMAND, cmd);
> > > >       }
> > > >       return 0;
> > > > --
> > > > 2.49.0.987.g0cc8ee98dc-goog
> > > >
> > >
> > > --
> > > மணிவண்ணன் சதாசிவம்