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

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Date:	Wed, 18 Jul 2012 15:59:31 -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 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?

-- Shuah


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