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

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Date:	Sat, 17 Sep 2011 09:23:29 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Vincent Palatin <vpalatin@...omium.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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 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?

Alan Stern

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