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

On commit 39c90ece7565f5c47110c2fa77409d7a9478bd5b:

	[IPV4]: Convert rt_check_expire() from softirq processing to workqueue.

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 45651834e1e2..1bff9ed349ff 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -578,6 +578,9 @@ 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));