Date: Mon, 9 Dec 2002 11:17:59 +0100 (CET) From: steff@tdc.dk To: FreeBSD-gnats-submit@FreeBSD.org Cc: steff@tdc.dk Subject: standards/46119: Priority problems for SCHED_OTHER using pthreads Message-ID: <200212091017.gB9AHxoc012767@qostest.ip.tele.dk>
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>Number: 46119
>Category: standards
>Synopsis: Priority problems for SCHED_OTHER using pthreads
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-standards
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Mon Dec 09 02:20:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Steffen Schumacher
>Release: FreeBSD 4.6.1-RC2 i386
>Organization:
TDC Tele Danmark A/S
>Environment:
Tested on two platforms..
System: FreeBSD XxXxX.ip.tele.dk 4.6.1-RC2 FreeBSD 4.6.1-RC2 #0: Thu Jul 18 08:24:45 GMT 2002 root@freebsd-stable.sentex.ca:/usr/src/sys/compile/GENERIC i386
Pentium 3 750 MHz, 384 MB ram (basic home office pc)
System2: FreeBSD xXxXxX.ip.tele.dk 4.7-STABLE FreeBSD 4.7-STABLE #1: Tue Oct 29 16:24:29 CET 2002 root@xXxXxXxX.ip.tele.dk:/usr/src/sys/compile/QOSRC i386
Intel XEON 2.4 GHz, 1GB ram (Rack-server type pc)
>Description:
The POSIX functions sched_get_priority_max and sched_get_priority_min, is used for retrieving the max and min priority for a given scheduling policy.
When you compile and execute a C++ program containing the line {cout << "max SCHED_OTHER = " << sched_get_priority_max(SCHED_OTHER)
<< ", min SCHED_OTHER = " << sched_get_priority_min(SCHED_OTHER) << endl;} the output is "max SCHED_OTHER = 20, , min SCHED_OTHER = -20".
However, when I try to set the priority for a pthread_attr_t to anything not within the range [0:31], the value is reset to 15. This suggests that
fx. -15 is not a valid value for the priority of a SCHED_OTHER policed thread, even though the POSIX functions sched_get_priority_min/max has a
different opinion. I've tried to bypass the routines that set the priority for the pthread_attr_t-object using a sort of hack, and this actually
enables me to set the value to what ever I wan't (since I'm bypassing any kind of errorchecking). But when I attempt to create a thread using this
pthread_attr_t-object the core is dumped. So basically, I can't create threads with priorities other then [0:31] eventhough sched_get_priority_min/max
says I should be able to.
>How-To-Repeat:
#include <iostream.h>
#include <pthread.h>
#include <errno.h>
#include <time.h>
//This is our own copy of the struct defined in the freebsd-cvs repository, in the pthread library, prefixed with 'snuf_'
struct snuf_pthread_attr {
int sched_policy;
int sched_inherit;
int sched_interval;
int prio;
int suspend;
int flags;
void *arg_attr;
void (*cleanup_attr) ();
void *stackaddr_attr;
size_t stacksize_attr;
size_t guardsize_attr;
};
void main()
{
pthread_t dummy;
pthread_attr_t p_attr;
struct sched_param schedparam;
pthread_attr_init(&p_attr);
pthread_attr_setdetachstate(&p_attr,PTHREAD_CREATE_DETACHED);
pthread_attr_setinheritsched(&p_attr,PTHREAD_EXPLICIT_SCHED);
int code = pthread_attr_setschedpolicy(&p_attr, SCHED_OTHER);
if ( code != 0 )
{
printf("Policy couldn't be set: %d\n", code );
if ( code == EINVAL )
{
printf( "[EINVAL].\n" );
exit( 0 );
}
if ( code == ENOTSUP )
{
printf( "[ENOTSUP].\n" );
exit( 0 );
}
}
cout << "max SCHED_OTHER = " << sched_get_priority_max(SCHED_OTHER) << ", min SCHED_OTHER = " << sched_get_priority_min(SCHED_OTHER) << endl;
schedparam.sched_priority = -15; //Attempting to set priority to -15
pthread_attr_setschedparam(&p_attr, &schedparam);
if ( code != 0 )
{
printf("pthread_attr_setschedparam failed: %d\n", code );
if ( code == EINVAL )
{
printf( "[EINVAL].\n" );
exit( 0 );
}
if ( code == ENOTSUP )
{
printf( "[ENOTSUP].\n" );
exit( 0 );
}
}
//Read the value of the structmember prio using the snuf-struct..
cout << "address: " << p_attr << " prio would be: " << ((snuf_pthread_attr *)(p_attr))->prio << endl;
//You can attempt to set the value of prio without any of the errorchecking provided by pthread_attr_setschedparam function
//but this should first be attempted when you've certified that the pthread_attr_setschedparam isn't able to set the priovalue
//to anything other then [0:31]
//((snuf_pthread_attr *)(p_attr))->prio = 0;
//Reading the value of the parameter:
code = pthread_attr_getschedparam(&p_attr, &schedparam);
if ( code != 0 )
{
printf("Thread pthread_attr_getschedparam Failed: %d\n", code );
if ( code == EINVAL )
{
printf( "[EINVAL] -> Report this as a bug.\n" );
exit( 0 );
}
}
cout << "Read the schedparam.prio to: " << schedparam.priority << endl;
cout << "CREATING THREAD NOW!!!!\n";
code = pthread_create(&dummy, &p_attr, (void *(*)(void*))(INSERT_YOUR_OWN_FUNCTION_HERE), (void*)0);
if ( code != 0 )
{
printf("Thread Creation Failed: %d\n", code );
if ( code == EAGAIN )
{
printf( "[EAGAIN] -> Report this as a bug.\n" );
exit( 0 );
}
}
pthread_attr_destroy(&p_attr);
sleep(10); //Sleeping so that the program doesn't exit right away..
}
>Fix:
Well that really depends wether its the sched_get_priority_min/max macros that is incorrect or its the core functions of freeBSD.
My knowledge of FreeBSD or any kind of UNIX type-OS dates only 4 months back, so I'm not really the right person to ask about this.
>Release-Note:
>Audit-Trail:
>Unformatted:
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