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From: hue@netcom.UUCP (Jonathan Hue)
Newsgroups: comp.os.mach
Subject: Mach context switch time
Message-ID: <2895@netcom.UUCP>
Date: 12 Oct 89 04:54:03 GMT
Organization: NetCom- The Bay Area's Public Access Unix System {408 997-9175 guest}
Lines: 94


>        Mean real time per context switch, corresponding context switch rate:
>
>        PDP-11/45       EPOS              170 usec      5,882 / sec
>        DECStation 3100 ULTRIX 2.0 R7     390           2,654
>        Sun 4/280       SunOs Sys4-3.2R2  623           1,605
>        VAX 8650        BSD 4.3           723           1,383
>        NeXt            MACH              873           1,145

The following program executes the loop 10000 times in 7.3 seconds on a
NeXT.  Each time through the loop is 2 context switches, so this works
out to 2740 context switches/sec, or 365us per context switch.

#include <sys/types.h>
#include <stdio.h>
#include <mach.h>
#include <sys/message.h>

struct mymsg
{
    msg_header_t	my_header;
    msg_type_t		my_type;
};

main(argc, argv)
int argc;
char **argv;
{
    register int iterations=1;
    register kern_return_t error;
    port_t port, newport;
    unsigned int num_ports;
    struct mymsg msg;
    port_t port_set[10];
    port_array_t new_set;

    if (argc == 2)
	iterations = atoi(*++argv);
    if ((error = port_allocate(task_self(), &port)) != KERN_SUCCESS)
	mach_error("port_allocate", error);
    if ((error = port_set_backlog(task_self(), port, 10)) != KERN_SUCCESS)
	mach_error("port_set_backlog", error);
    port_set[0] = port;
    mach_ports_register(task_self(), port_set, 1);
    switch (fork())
    {
	case -1:
	    perror("fork");
	    exit(1);
	case 0:
	    mach_ports_lookup(task_self(), &new_set, &num_ports);
	    port = *new_set;
	    msg.my_header.msg_remote_port = port;
	    if ((error = port_allocate(task_self(), &newport)) != KERN_SUCCESS)
		mach_error("port_allocate", error);
	    msg.my_header.msg_remote_port = port;
	    msg.my_header.msg_local_port = newport;
	    msg.my_header.msg_id = 0xc0ffee;
	    msg.my_header.msg_size = sizeof(msg);
	    msg.my_header.msg_type = MSG_TYPE_NORMAL;
	    msg.my_header.msg_simple = TRUE;
	    
	    msg.my_type.msg_type_name = MSG_TYPE_INTEGER_32;
	    msg.my_type.msg_type_size = 32;
	    msg.my_type.msg_type_number = 0;
	    msg.my_type.msg_type_inline = TRUE;
	    msg.my_type.msg_type_longform = FALSE;
	    msg.my_type.msg_type_deallocate = FALSE;
	    while (--iterations != -1)
	    {
		if ((error = msg_rpc(&(msg.my_header), SEND_SWITCH,
				     sizeof(msg), 0, 0)) != RPC_SUCCESS)
		    mach_error("msg_send", error);
	    }
	    exit(0);
	default:
	    msg.my_header.msg_local_port = port;
	    msg.my_header.msg_size = sizeof(msg);
	    while (--iterations != -1)
	    {
		if ((error = msg_receive(&(msg.my_header), MSG_OPTION_NONE, 0))
		    != RCV_SUCCESS)
		    mach_error("msg_receive", error);
		if ((error = msg_send(&(msg.my_header), SEND_SWITCH, 0)) !=
		     SEND_SUCCESS)
		    mach_error("msg_receive", error);
	    }
	    break;
    }
    wait(0);
}


-Jonathan