From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 3 Jan 2012 00:00:11 +0000 (+0000)
Subject: net_sched: qdisc_alloc_handle() can be too slow
X-Git-Tag: v3.3-rc1~182^2~47
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fa0f5aa74316c636427ac92dad0bc5714c34ca17;p=pandora-kernel.git

net_sched: qdisc_alloc_handle() can be too slow

When trying to allocate ~32768 qdiscs using autohandle mechanism, we can
fill the space managed by kernel (handles in [8000-FFFF]:0000 range)

But O(N^2) qdisc_alloc_handle() loops 0x10000 times instead of 0x8000

time tc add qdisc add dev eth0 parent 10:7fff pfifo limit 10
RTNETLINK answers: Cannot allocate memory
real    1m54.826s
user    0m0.000s
sys     0m0.004s

INFO: rcu_sched_state detected stall on CPU 0 (t=60000 jiffies)

Half number of loops, and add a cond_resched() call.
We hold rtnl at this point.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Dave Taht <dave.taht@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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