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Date: Wed, 18 Jul 2012 17:32:29 -0600 From: Toshi Kani <toshi.kani@...com> To: Joe Perches <joe@...ches.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 15:49 -0700, Joe Perches wrote: > 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, > }; > Hi Joe, I thought about using stack initially, but I too was not sure how big the buffer size should be, and was a bit afraid of causing kernel stack overflow potentially. Since it is mainly used for error paths in ACPI hotplug handlers, I do not think alloc/free can lead any performance impact. Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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