netdev - [PATCH net-next] net_sched: qdisc_alloc

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Date:	Tue, 03 Jan 2012 10:58:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>, Dave Taht <dave.taht@...il.com>
Subject: [PATCH net-next] 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@...il.com>
CC: Dave Taht <dave.taht@...il.com>
---
Next move is using rb-tree instead of a linked list, to speedup
qdisc_lookup(). A complex qdisc setup is way too slow.

 net/sched/sch_api.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)


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