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

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Message-ID: <CAE9FiQWwn1B0DyXVA9GiWhUr9kdeH9fVoE73UjBOwE2nqDNEVQ@mail.gmail.com>
Date:	Wed, 21 Sep 2011 11:22:50 -0700
From:	Yinghai Lu <yinghai.lu@...cle.com>
To:	Vincent Palatin <vpalatin@...omium.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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 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.

Yinghai
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