linux-kernel - Re: [PATCH 1/4] ACPI: Add acpi_pr

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Date:	Wed, 18 Jul 2012 16:40:57 -0600
From:	Shuah Khan <shuah.khan@...com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	lenb@...nel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
	isimatu.yasuaki@...fujitsu.com, liuj97@...il.com,
	srivatsa.bhat@...ux.vnet.ibm.com, prarit@...hat.com,
	imammedo@...hat.com, vijaymohan.pandarathil@...com,
	shuahkhan@...il.com
Subject: Re: [PATCH 1/4] ACPI: Add acpi_pr_<level>() interfaces

On Wed, 2012-07-18 at 16:26 -0600, Toshi Kani wrote:
> On Wed, 2012-07-18 at 15:59 -0600, Shuah Khan wrote:
> > On Wed, 2012-07-18 at 14:40 -0600, Toshi Kani wrote:
> > > This patch introduces acpi_pr_<level>(), where <level> is a message
> > > level such as err/warn/info, to support improved logging messages
> > > for ACPI, esp. in hotplug operations.  acpi_pr_<level>() appends
> > > "ACPI" prefix and ACPI object path to the messages.  This improves
> > > diagnostics in hotplug operations since it identifies an object that
> > > caused an issue in a log file.
> > > 
> > > acpi_pr_<level>() takes acpi_handle as an argument, which is passed
> > > to ACPI hotplug notify handlers from the ACPI CA.  Therefore, it is
> > > always available unlike other kernel objects, such as device.
> > > 
> > > For example, the statement below
> > >   acpi_pr_err(handle, "Device don't exist, dropping EJECT\n");
> > > logs an error message like this:
> > >   ACPI: \_SB_.SCK4.CPU4: Device don't exist, dropping EJECT
> > > 
> > > Signed-off-by: Toshi Kani <toshi.kani@...com>
> > > ---
> > >  drivers/acpi/utils.c    |   32 ++++++++++++++++++++++++++++++++
> > >  include/acpi/acpi_bus.h |   18 ++++++++++++++++++
> > >  2 files changed, 50 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> > > index 3e87c9c..4097266 100644
> > > --- a/drivers/acpi/utils.c
> > > +++ b/drivers/acpi/utils.c
> > > @@ -454,3 +454,35 @@ acpi_evaluate_hotplug_ost(acpi_handle handle, u32 source_event,
> > >  #endif
> > >  }
> > >  EXPORT_SYMBOL(acpi_evaluate_hotplug_ost);
> > > +
> > > +/**
> > > + * acpi_printk: Print messages with ACPI prefix and object path
> > > + *
> > > + * This function is intended to be called through acpi_pr_<level> macros.
> > > + */
> > > +void
> > > +acpi_printk(const char *level, acpi_handle handle, const char *fmt, ...)
> > > +{
> > > +	struct va_format vaf;
> > > +	va_list args;
> > > +	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER};
> > > +	char *path;
> > > +	acpi_status ret;
> > > +
> > > +	va_start(args, fmt);
> > > +
> > > +	vaf.fmt = fmt;
> > > +	vaf.va = &args;
> > > +
> > > +	ret = acpi_get_name(handle, ACPI_FULL_PATHNAME, &buffer);
> > 
> > One big problem I see with this approach is now each acpi_printk() will
> > result in a call to acpi_get_name() which will invoke several ACPI
> > calls, including a call to acpi_ut_initialize_buffer() which allocates
> > buffer. Is this really warranted? What is the performance impact of this
> > change?
> 
> Hi Shuah,
> 
> This interface is intended to be used by acpi_pr_<level>(), which is
> used for error, warning, debugging, etc.  It is not intended to be used
> in any performance path.
> 

How does one enable this interface to see errors, warns, debugging? Is
there a special mode kernel needs to run in? I am trying to understand
what you mean by "not intended to be used in any performance path". Does
one build a special kernel similar to CONFIG_VM_DEBUG (just happen to
the one I could think off) ?

-- Shuah

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