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

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Date:	Wed, 18 Jul 2012 15:49:41 -0700
From:	Joe Perches <joe@...ches.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	shuah.khan@...com, 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.
[]
> > > diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
[]
> > > @@ -454,3 +454,35 @@ acpi_evaluate_hotplug_ost(acpi_handle handle, u32 source_event,
[]
> > > +	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER};
[]
> > > +	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?
[]
> 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.

While it's not performance critical, perhaps the buffer
alloc/free could be avoided by using stack. Something like:

	char name[ACPI_PATH_SEGMENT_LENGTH * max_segments ? ];
	struct acpi_buffer buffer = {
		.length = ACPI_PATH_SEGMENT_LENGTH,
		.buffer = name,
	};


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