Measuring the correctness of ndelay() function. Post: 302969902

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Operating Systems Linux Ubuntu Measuring the correctness of ndelay() function. Post 302969902 by BHASKAR JUPUDI on Tuesday 29th of March 2016 06:31:47 PM

03-29-2016

Registered User

Measuring the correctness of ndelay() function.

I wrote this kernel module to test the correctness of ndelay() function.

Kernel mdoule:

Code:

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/time.h>
#include <linux/delay.h>
static int __init initialize(void)
{
	ktime_t start, end;
	s64 actual_time;
	int i;
	for(i=0;i<1000;i++)
	{
		start = ktime_get();
			ndelay(100);			
		end = ktime_get();
		actual_time = ktime_to_ns(ktime_sub(end, start));
		printk("%lld\n",(long long)actual_time);	
	}
	return 0;
}

static void __exit final(void)
{
     printk(KERN_INFO "Unload module\n");
}

module_init(initialize);
module_exit(final);

MODULE_AUTHOR("Bhaskar");
MODULE_DESCRIPTION("looping for 1000 times");
MODULE_LICENSE("GPL");

The output of dmesg:

Code:

[ 1028.135657] 379
[ 1028.135659] 383
[ 1028.135661] 370
[ 1028.135663] 372
[ 1028.135665] 332
[ 1028.135667] 348
[ 1028.135668] 318
[ 1028.135670] 365
[ 1028.135672] 350
[ 1028.135674] 327
[ 1028.135676] 359
[ 1028.135677] 358
[ 1028.135679] 320
[ 1028.135681] 393
[ 1028.135683] 359
[ 1028.135685] 357
[ 1028.135687] 361
[ 1028.135688] 325
[ 1028.135690] 360
[ 1028.135692] 302
[ 1028.135694] 353
[ 1028.135696] 375
[ 1028.135698] 342
[ 1028.135700] 377
[ 1028.135702] 382
[ 1028.135704] 390
[ 1028.135706] 322
[ 1028.135707] 361
[ 1028.135709] 392
[ 1028.135711] 387

Here my question is I'm trying to measure 100ns delay, but I'm getting output in 300's. One of the possible things that can happen is storing the value of ktime_get() into end module is taking some time. So can anyone please suggest me alternative or where I'm going wrong.

BHASKAR JUPUDI

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template::xml

Template::XML(3pm)					User Contributed Perl Documentation					Template::XML(3pm)

NAME

       Template::XML - XML plugins for the Template Toolkit

SYNOPSIS

	   [% USE XML;

	      dom    = XML.dom('foo.xml');
	      xpath  = XML.xpath('bar.xml');
	      simple = XML.simple('baz.xml');
	      rss    = XML.simple('news.rdf');
	   %]

DESCRIPTION

       The Template-XML distribution provides a number of Template Toolkit plugin modules for working with XML.

       The Template::Plugin::XML module is a front-end to the various other XML plugin modules.  Through this you can access XML files and direc-
       tories of XML files via the Template::Plugin::XML::File and Template::Plugin::XML::Directory modules (which subclass from the Tem-
       plate::Plugin::File and Template::Plugin::Directory modules respectively).  You can then create a Document Object Model (DOM) from an XML
       file (Template::Plugin::XML::DOM), examine it using XPath queries (Template::Plugin::XML::XPath), turn it into a Perl data structure (Tem-
       plate::Plugin::XML::Simple) or parse it as an RSS (RDF Site Summary) file.

       The basic XML plugins were distributed as part of the Template Toolkit until version 2.15 released in May 2006.	At this time they were
       extracted into this separate Template-XML distribution and an alpha version of this Template::Plugin::XML front-end module was added.

AUTHORS

       Andy Wardley wrote the Template Toolkit plugin modules, with assistance from Simon Matthews in the case of the XML::DOM plugin.	Matt
       Sergeant wrote the XML::XPath module.  Enno Derksen and Clark Cooper wrote the XML::DOM module.	Jonathan Eisenzopf wrote the XML::RSS mod-
       ule.  Grant McLean wrote the XML::Simple module.  Clark Cooper and Larry Wall wrote the XML::Parser module.  James Clark wrote the expat
       library.

COPYRIGHT

       Copyright (C) 1996-2006 Andy Wardley.  All Rights Reserved.

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

       Template, Template::Plugins, Template::Plugin::XML, Template::Plugin::XML::DOM, Template::Plugin::XML::RSS, Template::Plugin::XML::Simple,
       Template::Plugin::XML::XPath

perl v5.8.8							    2008-03-01							Template::XML(3pm)