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

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Date:	Wed, 21 Sep 2011 10:24:01 -0700
From:	Vincent Palatin <vpalatin@...omium.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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 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.

-- 
Vincent
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