内容简介
int ioprio_get(int which, int who) int ioprio_set(int which, int who, int ioprio) |
描述
ioprio_get() and%uA0ioprio_set()%uA0系统调用分别获取和设置一个或多个进程的I / O调度类和优先级。The%uA0which%uA0and%uA0who%uA0arguments identify the process(es) on which the system calls operate. The%uA0which%uA0argument determines how%uA0who%uA0is interpreted, and has one of the following values:
| 标签 | 描述 |
|---|---|
| IOPRIO_WHO_PROCESS | |
| %uA0 | who%uA0is a process ID identifying a single process. |
| IOPRIO_WHO_PGRP | |
| %uA0 | who%uA0is a process group ID identifying all the members of a process group. |
| IOPRIO_WHO_USER | |
| %uA0 | who%uA0is a user ID identifying all of the processes that have a matching real UID. |
|
If%uA0which%uA0is specified as%uA0IOPRIO_WHO_PGRP%uA0or%uA0IOPRIO_WHO_USER%uA0when callingioprio_get(), and more than one process matches%uA0who, then the returned priority will be the highest one found among all of the matching processes. One priority is said to be higher than another one if it belongs to a higher priority class (IOPRIO_CLASS_RT%uA0is the highest priority class%uA0IOPRIO_CLASS_IDLE%uA0is the lowest) or if it belongs to the same priority class as the other process but has a higher priority level (a lower priority number means a higher priority level).
The%uA0ioprio%uA0argument given to%uA0ioprio_set() is a bit mask that specifies both the scheduling class and the priority to be assigned to the target process(es). The following macros are used for assembling and dissecting%uA0ioprio%uA0values: |
|
| IOPRIO_PRIO_VALUE(class,%uA0data) | |
| %uA0 | Given a scheduling%uA0class%uA0and priority (data), this macro combines the two values to produce an%uA0ioprio%uA0value, which is returned as the result of the macro. |
| IOPRIO_PRIO_CLASS(mask) | |
| %uA0 | Given%uA0mask%uA0(an%uA0ioprio%uA0value), this macro returns its I/O class component, that is, one of the values%uA0IOPRIO_CLASS_RT,IOPRIO_CLASS_BE, or%uA0IOPRIO_CLASS_IDLE. |
| IOPRIO_PRIO_DATA(mask) | |
| %uA0 | Given%uA0mask%uA0(an%uA0ioprio%uA0value), this macro returns its priority (data) component. |
I/O priorities are supported for reads and for synchronous (O_DIRECT, O_SYNC) writes. I/O priorities are not supported for asynchronous writes because they are issued outside the context of the program dirtying the memory, and thus program-specific priorities do not apply.
返回值
On success,%uA0ioprio_get() returns the%uA0ioprio%uA0value of the process with highest I/O priority of any of the processes that match the criteria specified in%uA0which%uA0and%uA0who. On error, -1 is returned, and%uA0errno%uA0is set to indicate the error.On success,%uA0ioprio_set() returns 0. On error, -1 is returned, and%uA0errno%uA0is set to indicate the error.
错误
| 标签 | 描述 |
|---|---|
| EPERM | The calling process does not have the privilege needed to assign this%uA0ioprio%uA0to the specified process(es). See the NOTES section for more information on required privileges forioprio_set(). |
| ESRCH | No process(es) could be found that matched the specification inwhich%uA0and%uA0who. |
| EINVAL | Invalid value for%uA0which%uA0or%uA0ioprio. Refer to the NOTES section for available scheduler classes and priority levels for%uA0ioprio. |
VERSIONS
These system calls have been available on Linux since kernel 2.6.13.遵循于
这些系统调用是Linux特有的。注意
Glibc does not provide wrapper for these system calls call them using%uA0syscall(2).These system calls only have an effect when used in conjunction with an I/O scheduler that supports I/O priorities. As at kernel 2.6.17 the only such scheduler is the Completely Fair Queuing (CFQ) I/O scheduler.
Selecting an I/O Scheduler
I/O Schedulers are selected on a per-device basis via the special file/sys/block/<device>/queue/scheduler.One can view the current I/O scheduler via the%uA0/sys%uA0file system. For example, the following command displays a list of all schedulers currently loaded in the kernel:
$ cat /sys/block/hda/queue/scheduler noop anticipatory deadline [cfq] |
The scheduler surrounded by brackets is the one actually in use for the device (hda%uA0in the example). Setting another scheduler is done by writing the name of the new scheduler to this file. For example, the following command will set the scheduler for thehdaꃞvice to%uA0cfq:
$ su Password: # echo cfq > /sys/block/hda/queue/scheduler |
完全公平队列（CFQ）的I / O调度
Since v3 (aka CFQ Time Sliced) CFQ implements I/O nice levels similar to those of CPU scheduling. These nice levels are grouped in three scheduling classes each one containing one or more priority levels:| 标签 | 描述 |
|---|---|
| IOPRIO_CLASS_RT%uA0(1) | |
| %uA0 | This is the real-time I/O class. This scheduling class is given higher priority than any other class: processes from this class are given first access to the disk every time. Thus this I/O class needs to be used with some care: one I/O real-time process can starve the entire system. Within the real-time class, there are 8 levels of class data (priority) that determine exactly how much time this process needs the disk for on each service. The highest real-time priority level is 0 the lowest is 7. In the future this might change to be more directly mappable to performance, by passing in a desired data rate instead. |
| IOPRIO_CLASS_BE%uA0(2) | |
| %uA0 | This is the best-effort scheduling class, which is the default for any process that hasn’t set a specific I/O priority. The class data (priority) determines how much I/O bandwidth the process will get. Best-effort priority levels are analogous to CPU nice values (see%uA0getpriority(2)). The priority level determines a priority relative to other processes in the best-effort scheduling class. Priority levels range from 0 (highest) to 7 (lowest). |
| IOPRIO_CLASS_IDLE%uA0(3) | |
| %uA0 | This is the idle scheduling class. Processes running at this level only get I/O time when no one else needs the disk. The idle class has no class data. Attention is required when assigning this priority class to a process, since it may become starved if higher priority processes are constantly accessing the disk. |
所需的权限设置I/ O优先级
权限更改进程的优先级被授予或拒绝基于两个参数：| 标签 | 描述 |
|---|---|
| Process ownership | |
| %uA0 | An unprivileged process may only set the I/O priority of a process whose real UID matches the real or effective UID of the calling process. A process which has the%uA0CAP_SYS_NICEcapability can change the priority of any process. |
| What is the desired priority | |
| %uA0 | Attempts to set very high priorities (IOPRIO_CLASS_RT) or very low ones (IOPRIO_CLASS_IDLE) require theCAP_SYS_ADMINꃊpability. |