Re: [PATCH 1/4] ACPI: Add acpi_pr_() interfaces

Shuah Khan
2012-07-18T22:41:08Z

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@hp.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