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mips-mt-fpaff.c

/*
 * 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/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 = 0;

/*
 * 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;
}


/*
 * 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_t new_mask;
      cpumask_t effective_mask;
      int retval;
      struct task_struct *p;
      struct thread_info *ti;

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

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

      get_online_cpus();
      read_lock(&tasklist_lock);

      p = find_process_by_pid(pid);
      if (!p) {
            read_unlock(&tasklist_lock);
            put_online_cpus();
            return -ESRCH;
      }

      /*
       * It is not safe to call set_cpus_allowed with the
       * tasklist_lock held.  We will bump the task_struct's
       * usage count and drop tasklist_lock before invoking
       * set_cpus_allowed.
       */
      get_task_struct(p);

      retval = -EPERM;
      if ((current->euid != p->euid) && (current->euid != p->uid) &&
                  !capable(CAP_SYS_NICE)) {
            read_unlock(&tasklist_lock);
            goto out_unlock;
      }

      retval = security_task_setscheduler(p, 0, NULL);
      if (retval)
            goto out_unlock;

      /* Record new user-specified CPU set for future reference */
      p->thread.user_cpus_allowed = new_mask;

      /* Unlock the task list */
      read_unlock(&tasklist_lock);

      /* 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(p, effective_mask);
      } else {
            clear_ti_thread_flag(ti, TIF_FPUBOUND);
            retval = set_cpus_allowed(p, new_mask);
      }

out_unlock:
      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;

      cpus_and(mask, p->thread.user_cpus_allowed, cpu_possible_map);

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);

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