linux-kernel - Re: [PATCH v5 RESEND 1/5] ACPI: Add acpi_pr

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Date:	Tue, 20 Nov 2012 02:17:27 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-acpi@...r.kernel.org, lenb@...nel.org,
	linux-kernel@...r.kernel.org, joe@...ches.com, bhelgaas@...gle.com,
	isimatu.yasuaki@...fujitsu.com, vijaymohan.pandarathil@...com,
	imammedo@...hat.com, prarit@...hat.com
Subject: Re: [PATCH v5 RESEND 1/5] ACPI: Add acpi_pr_<level>() interfaces

On Monday, November 19, 2012 09:10:58 AM Rafael J. Wysocki wrote:
> On Tuesday, November 06, 2012 08:02:06 AM Toshi Kani wrote:
> > This patch introduces acpi_pr_<level>(), where <level> is a kernel
> > message level such as err/warn/info, to support improved logging
> > messages for ACPI, esp. for hotplug operations.  acpi_pr_<level>()
> > appends "ACPI" prefix and ACPI object path to the messages.  This
> > improves diagnosis of hotplug operations since an error message in
> > a log file identifies an object that caused an issue.
> > 
> > acpi_pr_<level>() takes acpi_handle as an argument, which is passed
> > to ACPI hotplug notify handlers from the ACPICA.  Therefore, it is
> > always available unlike other kernel objects, such as device.
> > 
> > For example:
> >   acpi_pr_err(handle, "Device don't exist, dropping EJECT\n");
> > logs an error message like this at KERN_ERR.
> >   ACPI: \_SB_.SCK4.CPU4: Device don't exist, dropping EJECT
> >
> > ACPI drivers can use acpi_pr_<level>() when they need to identify
> > a target ACPI object path in their messages, such as error cases.
> > The usage model is similar to dev_<level>().  acpi_pr_<level>() can
> > be used when device is not created/valid, which may be the case in
> > ACPI hotplug handlers.  ACPI object path is also consistent on the
> > platform, unlike device name that changes over hotplug operations.
> > 
> > ACPI drivers should use dev_<level>() when device is valid and
> > acpi_pr_<level>() is already used by the caller in its error path.
> > Device name provides more user friendly information.
> > 
> > ACPI drivers also continue to use pr_<level>() when messages do not
> > need to specify device information, such as boot-up messages.
> > 
> > Note: ACPI_[WARNING|INFO|ERROR]() are intended for the ACPICA and
> > are not associated with the kernel message level.
> 
> Well, the idea is generally good, but unfortunately acpi_get_name() is
> not a cheap operation.  Namely, it takes the global namespace mutex,
> so your acpi_printk() may be a source of serious contention on that
> lock if used excessively from concurrent threads.
> 
> Do you think you can address this problem?
> 
> Moreover, this also means that acpi_printk() cannot be used from interrupt
> context, so it is not a printk() replacement, which at least should be
> documented.

Unfortunately, I lost your reply to my previous message in this thread
due to my e-mail client malfunction.  Sorry about that.

What about calling them acpi_handle_printk() and acpi_handle_<level>,
respectively?  Then, if it is clearly documented that those things
acquire the global namespace mutex and are not suitable for interrupt
context, it should be OK.

And please take Joe's feedback into account. :-)

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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