On Tue, Jan 21, 2014 at 03:36:37PM +0100, Michael Kerrisk wrote: > Peter, Dario,
> Is someone (e.g., one of you) planning to write man pages for the new > sched_setattr() and sched_getattr() system calls? (Also, for the > future, please CC [email protected] on patches that change the > API, then those of us who don't follow LKML get a heads up about > upcoming API changes.) first draft, shamelessly stolen from SCHED_SETSCHEDULER(2). One note on both the original as well as the below: process is ambiguous, the syscalls actually apply to a single thread of a process, not the entire process. --- NAME sched_setattr, sched_getattr - set and get scheduling policy/attributes SYNOPSIS #include <sched.h> struct sched_attr { u32 size; u32 sched_policy; u64 sched_flags; /* SCHED_NORMAL, SCHED_BATCH */ s32 sched_nice; /* SCHED_FIFO, SCHED_RR */ u32 sched_priority; /* SCHED_DEADLINE */ u64 sched_runtime; u64 sched_deadline; u64 sched_period; }; int sched_setattr(pid_t pid, const struct sched_attr *attr); int sched_getattr(pid_t pid, const struct sched_attr *attr, unsigned int size); DESCRIPTION sched_setattr() sets both the scheduling policy and the associated attributes for the process whose ID is specified in pid. If pid equals zero, the scheduling policy and attributes of the calling process will be set. The interpretation of the argument attr depends on the selected policy. Currently, Linux supports the following "normal" (i.e., non-real-time) scheduling policies: SCHED_OTHER the standard "fair" time-sharing policy; SCHED_BATCH for "batch" style execution of processes; and SCHED_IDLE for running very low priority background jobs. The following "real-time" policies are also supported, for special time-critical applications that need precise control over the way in which runnable processes are selected for execution: SCHED_FIFO a first-in, first-out policy; SCHED_RR a round-robin policy; and SCHED_DEADLINE a deadline policy. The semantics of each of these policies are detailed below. sched_attr::size must be set to the size of the structure, as in sizeof(struct sched_attr), if the provided structure is smaller than the kernel structure, any additional fields are assumed '0'. If the provided structure is larger than the kernel structure, the kernel verifies all additional fields are '0' if not the syscall will fail with -E2BIG. sched_attr::sched_policy the desired scheduling policy. sched_attr::sched_flags additional flags that can influence scheduling behaviour. Currently as per Linux kernel 3.14: SCHED_FLAG_RESET_ON_FORK - resets the scheduling policy to: (struct sched_attr){ .sched_policy = SCHED_OTHER, } on fork(). is the only supported flag. sched_attr::sched_nice should only be set for SCHED_OTHER, SCHED_BATCH, the desired nice value [-20,19], see NICE(2). sched_attr::sched_priority should only be set for SCHED_FIFO, SCHED_RR, the desired static priority [1,99]. sched_attr::sched_runtime sched_attr::sched_deadline sched_attr::sched_period should only be set for SCHED_DEADLINE and are the traditional sporadic task model parameters. sched_getattr() queries the scheduling policy currently applied to the process identified by pid. If pid equals zero, the policy of the calling process will be retrieved. The size argument should reflect the size of struct sched_attr as known to userspace. The kernel fills out sched_attr::size to the size of its sched_attr structure. If the user provided structure is larger, additional fields are not touched. If the user provided structure is smaller, but the kernel needs to return values outside the provided space, the syscall will fail with -E2BIG. The other sched_attr fields are filled out as described in sched_setattr(). ${insert SCHED_* descriptions} SCHED_DEADLINE: Sporadic task model deadline scheduling SCHED_DEADLINE is an implementation of GEDF (Global Earliest Deadline First) with additional CBS (Constant Bandwidth Server). The CBS guarantees that tasks that over-run their specified budget are throttled and do not affect the correct performance of other SCHED_DEADLINE tasks. SCHED_DEADLINE tasks will fail FORK(2) with -EAGAIN Setting SCHED_DEADLINE can fail with -EINVAL when admission control tests fail. ${NOTE: should we change that to -EBUSY ? } Other than that its pretty much the same as the existing SCHED_SETSCHEDULER(2) page. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
