mips-mt-fpaff.c

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/*
 * General MIPS MT support routines, usable in AP/SP, SMVP, or SMTC kernels
 * Copyright (C) 2005 Mips Technologies, Inc
 */
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/cpumask.h>
#include <linux/delay.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/security.h>
#include <linux/types.h>
#include <asm/uaccess.h>

/*
 * CPU mask used to set process affinity for MT VPEs/TCs with FPUs
 */
cpumask_t mt_fpu_cpumask;

static int fpaff_threshold = -1;
unsigned long mt_fpemul_threshold;

/*
 * Replacement functions for the sys_sched_setaffinity() and
 * sys_sched_getaffinity() system calls, so that we can integrate
 * FPU affinity with the user's requested processor affinity.
 * This code is 98% identical with the sys_sched_setaffinity()
 * and sys_sched_getaffinity() system calls, and should be
 * updated when kernel/sched.c changes.
 */

/*
 * find_process_by_pid - find a process with a matching PID value.
 * used in sys_sched_set/getaffinity() in kernel/sched.c, so
 * cloned here.
 */
static inline struct task_struct *find_process_by_pid(pid_t pid)
{
    return pid ? find_task_by_vpid(pid) : current;
}

/*
 * check the target process has a UID that matches the current process's
 */
static bool check_same_owner(struct task_struct *p)
{
    const struct cred *cred = current_cred(), *pcred;
    bool match;

    rcu_read_lock();
    pcred = __task_cred(p);
    match = (cred->euid == pcred->euid ||
         cred->euid == pcred->uid);
    rcu_read_unlock();
    return match;
}

/*
 * mipsmt_sys_sched_setaffinity - set the cpu affinity of a process
 */
asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len,
                      unsigned long __user *user_mask_ptr)
{
    cpumask_var_t cpus_allowed, new_mask, effective_mask;
    struct thread_info *ti;
    struct task_struct *p;
    int retval;

    if (len < sizeof(new_mask))
        return -EINVAL;

    if (copy_from_user(&new_mask, user_mask_ptr, sizeof(new_mask)))
        return -EFAULT;

    get_online_cpus();
    rcu_read_lock();

    p = find_process_by_pid(pid);
    if (!p) {
        rcu_read_unlock();
        put_online_cpus();
        return -ESRCH;
    }

    /* Prevent p going away */
    get_task_struct(p);
    rcu_read_unlock();

    if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
        retval = -ENOMEM;
        goto out_put_task;
    }
    if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
        retval = -ENOMEM;
        goto out_free_cpus_allowed;
    }
    if (!alloc_cpumask_var(&effective_mask, GFP_KERNEL)) {
        retval = -ENOMEM;
        goto out_free_new_mask;
    }
    retval = -EPERM;
    if (!check_same_owner(p) && !capable(CAP_SYS_NICE))
        goto out_unlock;

    retval = security_task_setscheduler(p);
    if (retval)
        goto out_unlock;

    /* Record new user-specified CPU set for future reference */
    cpumask_copy(&p->thread.user_cpus_allowed, new_mask);

 again:
    /* Compute new global allowed CPU set if necessary */
    ti = task_thread_info(p);
    if (test_ti_thread_flag(ti, TIF_FPUBOUND) &&
        cpus_intersects(*new_mask, mt_fpu_cpumask)) {
        cpus_and(*effective_mask, *new_mask, mt_fpu_cpumask);
        retval = set_cpus_allowed_ptr(p, effective_mask);
    } else {
        cpumask_copy(effective_mask, new_mask);
        clear_ti_thread_flag(ti, TIF_FPUBOUND);
        retval = set_cpus_allowed_ptr(p, new_mask);
    }

    if (!retval) {
        cpuset_cpus_allowed(p, cpus_allowed);
        if (!cpumask_subset(effective_mask, cpus_allowed)) {
            /*
             * We must have raced with a concurrent cpuset
             * update. Just reset the cpus_allowed to the
             * cpuset's cpus_allowed
             */
            cpumask_copy(new_mask, cpus_allowed);
            goto again;
        }
    }
out_unlock:
    free_cpumask_var(effective_mask);
out_free_new_mask:
    free_cpumask_var(new_mask);
out_free_cpus_allowed:
    free_cpumask_var(cpus_allowed);
out_put_task:
    put_task_struct(p);
    put_online_cpus();
    return retval;
}

/*
 * mipsmt_sys_sched_getaffinity - get the cpu affinity of a process
 */
asmlinkage long mipsmt_sys_sched_getaffinity(pid_t pid, unsigned int len,
                      unsigned long __user *user_mask_ptr)
{
    unsigned int real_len;
    cpumask_t mask;
    int retval;
    struct task_struct *p;

    real_len = sizeof(mask);
    if (len < real_len)
        return -EINVAL;

    get_online_cpus();
    read_lock(&tasklist_lock);

    retval = -ESRCH;
    p = find_process_by_pid(pid);
    if (!p)
        goto out_unlock;
    retval = security_task_getscheduler(p);
    if (retval)
        goto out_unlock;

    cpumask_and(&mask, &p->thread.user_cpus_allowed, cpu_possible_mask);

out_unlock:
    read_unlock(&tasklist_lock);
    put_online_cpus();
    if (retval)
        return retval;
    if (copy_to_user(user_mask_ptr, &mask, real_len))
        return -EFAULT;
    return real_len;
}


static int __init fpaff_thresh(char *str)
{
    get_option(&str, &fpaff_threshold);
    return 1;
}
__setup("fpaff=", fpaff_thresh);

/*
 * FPU Use Factor empirically derived from experiments on 34K
 */
#define FPUSEFACTOR 2000

static __init int mt_fp_affinity_init(void)
{
    if (fpaff_threshold >= 0) {
        mt_fpemul_threshold = fpaff_threshold;
    } else {
        mt_fpemul_threshold =
            (FPUSEFACTOR * (loops_per_jiffy/(500000/HZ))) / HZ;
    }
    printk(KERN_DEBUG "FPU Affinity set after %ld emulations\n",
           mt_fpemul_threshold);

    return 0;
}
arch_initcall(mt_fp_affinity_init);