linux-kernel - Re: [RFC] PM / Runtime: decrease verbosity in kernel log

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Date:	Wed, 21 Sep 2011 20:28:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Yinghai Lu <yinghai.lu@...cle.com>
Cc:	Vincent Palatin <vpalatin@...omium.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Olof Johansson <olofj@...omium.org>,
	Sameer Nanda <snanda@...omium.org>,
	Ming Lei <tom.leiming@...il.com>, linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [RFC] PM / Runtime: decrease verbosity in kernel log

On Wednesday, September 21, 2011, Yinghai Lu wrote:
> On Wed, Sep 21, 2011 at 10:24 AM, Vincent Palatin <vpalatin@...omium.org> wrote:
> > On Mon, Sep 19, 2011 at 14:08, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> On Monday, September 19, 2011, Vincent Palatin wrote:
> >>> On Sat, Sep 17, 2011 at 09:23, Alan Stern <stern@...land.harvard.edu> wrote:
> >>> > On Fri, 16 Sep 2011, Vincent Palatin wrote:
> >>> >
> >>> >> When activating the PCI runtime PM on a laptop, my kernel log is filled with
> >>> >> messages such as the following ones and can be hardly read to find interesting
> >>> >> information:
> >>> >> ehci_hcd 0000:00:1d.7: PME# disabled
> >>> >> ehci_hcd 0000:00:1d.7: PCI INT A -> GSI 16 (level, low) -> IRQ 16
> >>> >> ehci_hcd 0000:00:1d.7: setting latency timer to 64
> >>> >> ehci_hcd 0000:00:1d.7: PCI INT A disabled
> >>> >> ehci_hcd 0000:00:1d.7: PME# enabled
> >>> >> ehci_hcd 0000:00:1d.7: BAR 0: set to [mem 0x92205000-0x922053ff] (PCI address [0x92205000-0x922053ff])
> >>> >> ehci_hcd 0000:00:1d.7: restoring config space at offset 0xf (was 0x100, writing 0x10b)
> >>> >> ehci_hcd 0000:00:1d.7: restoring config space at offset 0x1 (was 0x2900000, writing 0x2900002)
> >>> > ...
> >>> >
> >>> >> All those messages are triggered by the following cause, the laptop has a USB
> >>> >> 3G modem with USB autosuspend activated. The USB device will wake up about
> >>> >> every 30s to do some network related activities. Every time, the modem wakes
> >>> >> up this triggers the wake up of the attached EHCI/PCI USB host controller
> >>> >> which reconfigures its PCI interface, then everything go back to a suspended mode.
> >>> >>
> >>> >> Having the same 10 lines of log repeated is not really useful, but I probably
> >>> >> cannot totally remove them since there are somewhat useful for PCI hotplug
> >>> >> users and other PCI debugging.
> >>> >> So, my proposal is to create a new dev_printk macro : "dev_printk_norpm" which
> >>> >> outputs traces only when the device has not the runtime PM activated,
> >>> >> and guard those traces with it.
> >>> >> (cf the 2 patches in this thread as a PoC)
> >>> >
> >>> > Wouldn't it be easier just to change the existing messages to DEBUG
> >>> > level?  Or are they more important than that?
> >>>
> >>> Yes, I can simply replace all those printk by dev_dbg traces. For my
> >>> use case, it's perfect.
> >>> My main concern was people using PCI hotplug, I think, then, their log
> >>> will remain mostly silent when inserting a card, I don't know if this
> >>> is acceptable or not.
> >>
> >> I think they don't really need that information except for debugging, right?
> >
> > I think so.
> > I will send a new patch with dev_dbg in replacement of the noisy
> > printks for PCI messages.
> >
> 
> please use dev_printk(KERN_DEBUG,...) instead. otherwise will need
> recompile the kernel with DEBUG enabled
> to get debug message with debug in boot command line.

Hmm?  I thought that using dev_dbg() was the recommended way?

Rafael
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