[PATCH] sched: fix scheduling latencies for !PREEMPT kernels

This patch adds a handful of cond_resched() points to a number of key,
scheduling-latency related non-inlined functions.

This reduces preemption latency for !PREEMPT kernels.  These are scheduling
points complementary to PREEMPT_VOLUNTARY scheduling points (might_sleep()
places) - i.e.  these are all points where an explicit cond_resched() had
to be added.

Has been tested as part of the -VP patchset.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/exec.c

@@ -186,6 +186,7 @@ static int count(char __user * __user * argv, int max)
 			argv++;
 			if(++i > max)
 				return -E2BIG;
+			cond_resched();
 		}
 	}
 	return i;

fs/fs-writeback.c

@@ -378,6 +378,7 @@ sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
 			list_move(&inode->i_list, &sb->s_dirty);
 		}
 		spin_unlock(&inode_lock);
+		cond_resched();
 		iput(inode);
 		spin_lock(&inode_lock);
 		if (wbc->nr_to_write <= 0)

fs/select.c

@@ -240,6 +240,7 @@ int do_select(int n, fd_set_bits *fds, long *timeout)
 						retval++;
 					}
 				}
+				cond_resched();
 			}
 			if (res_in)
 				*rinp = res_in;

kernel/printk.c

@@ -284,6 +284,7 @@ int do_syslog(int type, char __user * buf, int len)
 			error = __put_user(c,buf);
 			buf++;
 			i++;
+			cond_resched();
 			spin_lock_irq(&logbuf_lock);
 		}
 		spin_unlock_irq(&logbuf_lock);
@@ -325,6 +326,7 @@ int do_syslog(int type, char __user * buf, int len)
 			c = LOG_BUF(j);
 			spin_unlock_irq(&logbuf_lock);
 			error = __put_user(c,&buf[count-1-i]);
+			cond_resched();
 			spin_lock_irq(&logbuf_lock);
 		}
 		spin_unlock_irq(&logbuf_lock);
@@ -340,6 +342,7 @@ int do_syslog(int type, char __user * buf, int len)
 					error = -EFAULT;
 					break;
 				}
+				cond_resched();
 			}
 		}
 		break;

mm/memory.c

@@ -1742,6 +1742,7 @@ do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	}
 	smp_rmb();  /* Prevent CPU from reordering lock-free ->nopage() */
 retry:
+	cond_resched();
 	new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, &ret);
 
 	/* no page was available -- either SIGBUS or OOM */

mm/slab.c

@@ -2836,7 +2836,7 @@ static void cache_reap(void *unused)
 next_unlock:
 		spin_unlock_irq(&searchp->spinlock);
 next:
-		;
+		cond_resched();
 	}
 	check_irq_on();
 	up(&cache_chain_sem);

mm/vmscan.c

@@ -361,6 +361,8 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
 		int may_enter_fs;
 		int referenced;
 
+		cond_resched();
+
 		page = lru_to_page(page_list);
 		list_del(&page->lru);
 
@@ -710,6 +712,7 @@ refill_inactive_zone(struct zone *zone, struct scan_control *sc)
 		reclaim_mapped = 1;
 
 	while (!list_empty(&l_hold)) {
+		cond_resched();
 		page = lru_to_page(&l_hold);
 		list_del(&page->lru);
 		if (page_mapped(page)) {