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

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Date:	Mon, 19 Sep 2011 12:20:45 -0400
From:	Vincent Palatin <vpalatin@...omium.org>
To:	Alan Stern <stern@...land.harvard.edu>
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 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.

-- 
Vincent Palatin
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