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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LEARN ABOUT DEBIAN

log::agent::channel::syslog

Agent::Channel::Syslog(3pm)				User Contributed Perl Documentation			       Agent::Channel::Syslog(3pm)

NAME

       Log::Agent::Channel::Syslog - syslog logging channel for Log::Agent::Logger

SYNOPSIS

	require Log::Agent::Channel::Syslog;

	my $channel = Log::Agent::Channel::Syslog->make(
	    # Specific attributes
	    -prefix	=> prefix,
	    -facility	=> "user",
	    -showpid	=> 1,
	    -socktype	=> "unix",
	    -logopt	=> "ndelay",
	);

DESCRIPTION

       The syslog logging channels directs operations to syslog() via the Sys::Syslog(3) interface.

       The creation routine make() takes the following switches:

       "-facility" => facility
	   Tell syslog() which facility to use (e.g. "user", "auth", "daemon").  Unlike the Sys::Syslog(3) interface, the facility is set once and
	   for all: every message logged through this channel will use the same facility.

       "-logopt" => syslog options
	   Specifies logging options, under the form of a string containing zero or more of the words ndelay, cons or nowait.

       "-prefix" => prefix
	   The prefix here is syslog's identification string.

       "-showpid" => flag
	   Set to true to have the PID of the process logged. It is false by default.

       "-socktype" => (unix | inet)
	   Specifies the logging socket type to use. The default behaviour is to use Sys:Syslog's default.

AUTHOR

       Raphael Manfredi <Raphael_Manfredi@pobox.com>

SEE ALSO

       Log::Agent::Logger(3).

perl v5.10.0							    2002-03-09					       Agent::Channel::Syslog(3pm)