Entnommen aus /usr/src/linux/Documentation/block/ioprio.txt von Jens Axboe axboe@suse.de (March 11 2005) und für syscall umgeschrieben.

• ionice.c
• ionice.c.orig

read:
ionice -p $PID

set:
ionice -n $IOPRIO -p $PID
ionice -c $IOPRIOCLASS -p $PID

execute:
ionice -n $IOPRIO $COMMAND
ionice -c $IOPRIOCLASS $COMMAND

IOPRIO = 0..7 (0: höchste Priorität/real time, 7: niedrigest Prio./idle)
IOCLASS = 1..3 (1: -n0, 2: -n4, 3: -n7)

Hier die Ergebnisse eines kleinen Performancetests:

Während relativ wenig Last vorliegt (kaum HDD-Aktivität)

spot bin # ionice -n7 hdparm -T -t /dev/hda

/dev/hda:
 Timing cached reads:   778 MB in  2.00 seconds = 388.71 MB/sec
 Timing buffered disk reads:   70 MB in  3.07 seconds =  22.79 MB/sec

spot bin # hdparm -T -t /dev/hda

/dev/hda:
 Timing cached reads:   596 MB in  2.00 seconds = 297.43 MB/sec
 Timing buffered disk reads:   62 MB in  3.02 seconds =  20.55 MB/sec

spot bin # ionice -n0 hdparm -T -t /dev/hda

/dev/hda:
 Timing cached reads:   772 MB in  2.00 seconds = 385.24 MB/sec
 Timing buffered disk reads:   66 MB in  3.09 seconds =  21.36 MB/sec

Während bei mir “find / -name ‘asdf’” lief (HDD-LED ständig am leuchten)

spot bin # ionice -n7 hdparm -T -t /dev/hda

/dev/hda:
 Timing cached reads:   760 MB in  2.00 seconds = 379.51 MB/sec
 Timing buffered disk reads:   28 MB in  3.38 seconds =   8.28 MB/sec

spot bin # hdparm -T -t /dev/hda

/dev/hda:
 Timing cached reads:   756 MB in  2.00 seconds = 377.37 MB/sec
 Timing buffered disk reads:   46 MB in  3.12 seconds =  14.73 MB/sec

spot bin # ionice -n0 hdparm -T -t /dev/hda

/dev/hda:
 Timing cached reads:   782 MB in  2.00 seconds = 390.84 MB/sec
 Timing buffered disk reads:   54 MB in  3.03 seconds =  17.80 MB/sec

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <getopt.h>
#include <unistd.h>
#include <sys/ptrace.h>
#include <asm/unistd.h>
#include <sys/syscall.h>
 
 
#if defined(__i386__)
#define __NR_ioprio_set         289
#define __NR_ioprio_get         290
#elif defined(__ppc__)
#define __NR_ioprio_set         273
#define __NR_ioprio_get         274
#elif defined(__x86_64__)
#define __NR_ioprio_set         251
#define __NR_ioprio_get         252
#elif defined(__ia64__)
#define __NR_ioprio_set         1274
#define __NR_ioprio_get         1275
#else
#error "Unsupported arch"
#endif
 
enum {
        IOPRIO_CLASS_NONE,
        IOPRIO_CLASS_RT,
        IOPRIO_CLASS_BE,
        IOPRIO_CLASS_IDLE,
};
 
enum {
        IOPRIO_WHO_PROCESS = 1,
        IOPRIO_WHO_PGRP,
        IOPRIO_WHO_USER,
};
 
#define IOPRIO_CLASS_SHIFT      13
 
const char *to_prio[] = { "none", "realtime", "best-effort", "idle", };
 
int main(int argc, char *argv[])
{
        int ioprio = 4, set = 0, ioprio_class = IOPRIO_CLASS_BE;
        int c, pid = 0;
 
        while ((c = getopt(argc, argv, "+n:c:p:")) != EOF) {
                switch (c) {
                case 'n':
                        ioprio = strtol(optarg, NULL, 10);
                        set = 1;
                        break;
                case 'c':
                        ioprio_class = strtol(optarg, NULL, 10);
                        set = 1;
                        break;
                case 'p':
                        pid = strtol(optarg, NULL, 10);
                        break;
                }
        }
 
        switch (ioprio_class) {
                case IOPRIO_CLASS_NONE:
                        ioprio_class = IOPRIO_CLASS_BE;
                        break;
                case IOPRIO_CLASS_RT:
                case IOPRIO_CLASS_BE:
                        break;
                case IOPRIO_CLASS_IDLE:
                        ioprio = 7;
                        break;
                default:
                        printf("bad prio class %d\n", ioprio_class);
                        return 1;
        }
 
        if (!set) {
                if (!pid && argv[optind])
                        pid = strtol(argv[optind], NULL, 10);
 
                ioprio = syscall(SYS_ioprio_get, IOPRIO_WHO_PROCESS, pid);
 
                printf("pid=%d, %d\n", pid, ioprio);
 
                if (ioprio == -1)
                        perror("ioprio_get");
                else {
                        ioprio_class = ioprio >> IOPRIO_CLASS_SHIFT;
                        ioprio = ioprio & 0xff;
                        printf("%s: prio %d\n", to_prio[ioprio_class], ioprio);
                }
        } else {
                if (syscall(SYS_ioprio_set, IOPRIO_WHO_PROCESS, pid, ioprio | ioprio_class << IOPRIO_CLASS_SHIFT) == -1) {
                        perror("ioprio_set");
                        return 1;
                }
 
                if (argv[optind])
                        execvp(argv[optind], &argv[optind]);
        }
 
        return 0;
}

7a8
> #include <sys/syscall.h>
9,10d9
< extern int sys_ioprio_set(int, int, int);
< extern int sys_ioprio_get(int, int);
28,30d26
< _syscall3(int, ioprio_set, int, which, int, who, int, ioprio);
< _syscall2(int, ioprio_get, int, which, int, who);
<
88c84
<               ioprio = ioprio_get(IOPRIO_WHO_PROCESS, pid);
---
>               ioprio = syscall(SYS_ioprio_get, IOPRIO_WHO_PROCESS, pid);
100c96
<               if (ioprio_set(IOPRIO_WHO_PROCESS, pid, ioprio | ioprio_class << IOPRIO_CLASS_SHIFT) == -1) {
---
>               if (syscall(SYS_ioprio_set, IOPRIO_WHO_PROCESS, pid, ioprio | ioprio_class << IOPRIO_CLASS_SHIFT) == -1) {