From: Michael S. Tsirkin <mst@mellanox.co.il>
Date: Mon, 9 Jan 2006 22:04:40 +0000 (-0800)
Subject: IB/mthca: prevent event queue overrun
X-Git-Tag: v2.6.16-rc1~172^2~12
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=92898522e3ee1a0ba54140aad1974d9e868f74ae;p=pandora-kernel.git

IB/mthca: prevent event queue overrun

I am seeing EQ overruns in SDP stress tests: if the CQ completion
handler arms a CQ, this could generate more EQEs, so that EQ will
never get empty and consumer index will never get updated.

This is similiar to what we have with command interface:
		/*
		 * cmd_event() may add more commands.
		 * The card will think the queue has overflowed if
		 * we don't tell it we've been processing events.
		 */
However, for completion events, we *don't* want to update the consumer
index on each event. So, perform EQ doorbell coalescing: allocate EQs
with some spare EQEs, and update once we run out of them.

The value 0x80 was selected to avoid any performance impact.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
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