[PATCH] NET : rt_check_expire() can take a long time, add a cond_resched()

[Eric Dumazet <dada1@cosmosbay.com>]

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On commit 39c90ece7565f5c47110c2fa77409d7a9478bd5b we converted 
rt_check_expire() from softirq to workqueue, allowing the function to perform 
all work it was supposed to do.

When the IP route cache is big, rt_check_expire() can take a long time to run.
(default settings : 20% of the hash table is scanned at each invocation)

Adding cond_resched() helps giving cpu to higher priority tasks if necessary.

Using a "if (need_resched())" test before calling "cond_resched();" is 
necessary to avoid spending too much time doing the resched check.
(My tests gave a time reduction from 88 ms to 25 ms per rt_check_expire() run 
on my i686 test machine)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>


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diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index a9471b7..f0b28f9 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -580,6 +580,9 @@ static void rt_check_expire(struct work_struct *work)
 		i = (i + 1) & rt_hash_mask;
 		rthp = &rt_hash_table[i].chain;
 
+		if (need_resched())
+			cond_resched();
+
 		if (*rthp == NULL)
 			continue;
 		spin_lock_bh(rt_hash_lock_addr(i));