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diff --git a/Documentation/block/ioprio.txt b/Documentation/block/ioprio.txt deleted file mode 100644 index 8ed8c59380b4..000000000000 --- a/Documentation/block/ioprio.txt +++ /dev/null @@ -1,183 +0,0 @@ -Block io priorities -=================== - - -Intro ------ - -With the introduction of cfq v3 (aka cfq-ts or time sliced cfq), basic io -priorities are supported for reads on files. This enables users to io nice -processes or process groups, similar to what has been possible with cpu -scheduling for ages. This document mainly details the current possibilities -with cfq; other io schedulers do not support io priorities thus far. - -Scheduling classes ------------------- - -CFQ implements three generic scheduling classes that determine how io is -served for a process. - -IOPRIO_CLASS_RT: This is the realtime io class. This scheduling class is given -higher priority than any other in the system, processes from this class are -given first access to the disk every time. Thus it needs to be used with some -care, one io RT process can starve the entire system. Within the RT class, -there are 8 levels of class data that determine exactly how much time this -process needs the disk for on each service. In the future this might change -to be more directly mappable to performance, by passing in a wanted data -rate instead. - -IOPRIO_CLASS_BE: This is the best-effort scheduling class, which is the default -for any process that hasn't set a specific io priority. The class data -determines how much io bandwidth the process will get, it's directly mappable -to the cpu nice levels just more coarsely implemented. 0 is the highest -BE prio level, 7 is the lowest. The mapping between cpu nice level and io -nice level is determined as: io_nice = (cpu_nice + 20) / 5. - -IOPRIO_CLASS_IDLE: This is the idle scheduling class, processes running at this -level only get io time when no one else needs the disk. The idle class has no -class data, since it doesn't really apply here. - -Tools ------ - -See below for a sample ionice tool. Usage: - -# ionice -c<class> -n<level> -p<pid> - -If pid isn't given, the current process is assumed. IO priority settings -are inherited on fork, so you can use ionice to start the process at a given -level: - -# ionice -c2 -n0 /bin/ls - -will run ls at the best-effort scheduling class at the highest priority. -For a running process, you can give the pid instead: - -# ionice -c1 -n2 -p100 - -will change pid 100 to run at the realtime scheduling class, at priority 2. - ----> snip ionice.c tool <--- - -#include <stdio.h> -#include <stdlib.h> -#include <errno.h> -#include <getopt.h> -#include <unistd.h> -#include <sys/ptrace.h> -#include <asm/unistd.h> - -extern int sys_ioprio_set(int, int, int); -extern int sys_ioprio_get(int, int); - -#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 - -static inline int ioprio_set(int which, int who, int ioprio) -{ - return syscall(__NR_ioprio_set, which, who, ioprio); -} - -static inline int ioprio_get(int which, int who) -{ - return syscall(__NR_ioprio_get, which, who); -} - -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 = 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 (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; -} - ----> snip ionice.c tool <--- - - -March 11 2005, Jens Axboe <jens.axboe@oracle.com> |