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IB/cm: Improve local id allocation

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The IB CM uses an idr for local id allocations, with a running counter
as start_id.  This fails to generate distinct ids if

1. An id is constantly created and destroyed
2. A chunk of ids just beyond the current next_id value is occupied

This in turn leads to an increased chance of connection request being
mis-detected as a duplicate, sometimes for several retries, until
next_id gets past the block of allocated ids. This has been observed
in practice.

As a fix, remember the last id allocated and start immediately above it.
This also fixes a problem with the old code, where next_id might
overflow and become negative.

Signed-off-by: Michael S. Tsirkin <mst@dev.mellanox.co.il>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
This commit is contained in:
Michael S. Tsirkin 2007-05-21 19:06:54 +03:00 committed by Roland Dreier
parent 518b1646f8
commit 9f81036c54
1 changed files with 3 additions and 1 deletions
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4
drivers/infiniband/core/cm.c
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@ -306,7 +306,9 @@ static int cm_alloc_id(struct cm_id_private *cm_id_priv)
do {
spin_lock_irqsave(&cm.lock, flags);
ret = idr_get_new_above(&cm.local_id_table, cm_id_priv,
next_id++, &id);
next_id, &id);
if (!ret)
next_id = ((unsigned) id + 1) & MAX_ID_MASK;
spin_unlock_irqrestore(&cm.lock, flags);
} while( (ret == -EAGAIN) && idr_pre_get(&cm.local_id_table, GFP_KERNEL) );