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

[Ingo Molnar]

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.

	Ingo

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@xxxxxxx>

--- linux/fs/exec.c.orig	
+++ linux/fs/exec.c	
@@ -184,6 +184,7 @@ static int count(char __user * __user * 
 			argv++;
 			if(++i > max)
 				return -E2BIG;
+			cond_resched();
 		}
 	}
 	return i;
--- linux/fs/fs-writeback.c.orig	
+++ linux/fs/fs-writeback.c	
@@ -366,6 +366,7 @@ sync_sb_inodes(struct super_block *sb, s
 			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)
--- linux/fs/select.c.orig	
+++ linux/fs/select.c	
@@ -239,6 +239,7 @@ int do_select(int n, fd_set_bits *fds, l
 						retval++;
 					}
 				}
+				cond_resched();
 			}
 			if (res_in)
 				*rinp = res_in;
--- linux/kernel/printk.c.orig	
+++ linux/kernel/printk.c	
@@ -280,6 +280,7 @@ int do_syslog(int type, char __user * bu
 			error = __put_user(c,buf);
 			buf++;
 			i++;
+			cond_resched();
 			spin_lock_irq(&logbuf_lock);
 		}
 		spin_unlock_irq(&logbuf_lock);
@@ -321,6 +322,7 @@ int do_syslog(int type, char __user * bu
 			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);
@@ -336,6 +338,7 @@ int do_syslog(int type, char __user * bu
 					error = -EFAULT;
 					break;
 				}
+				cond_resched();
 			}
 		}
 		break;
--- linux/mm/memory.c.orig	
+++ linux/mm/memory.c	
@@ -1516,6 +1516,7 @@ do_no_page(struct mm_struct *mm, struct 
 	}
 	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 */
--- linux/mm/slab.c.orig	
+++ linux/mm/slab.c	
@@ -2793,7 +2793,7 @@ static void cache_reap(void *unused)
 next_unlock:
 		spin_unlock_irq(&searchp->spinlock);
 next:
-		;
+		cond_resched();
 	}
 	check_irq_on();
 	up(&cache_chain_sem);
--- linux/mm/vmscan.c.orig	
+++ linux/mm/vmscan.c	
@@ -361,6 +361,8 @@ static int shrink_list(struct list_head 
 		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, 
 		reclaim_mapped = 1;
 
 	while (!list_empty(&l_hold)) {
+		cond_resched();
 		page = lru_to_page(&l_hold);
 		list_del(&page->lru);
 		if (page_mapped(page)) {