netdev - Re: network devices don't handle pci_dma_mapping

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Date:	Wed, 06 Dec 2006 17:13:17 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...l.org
Cc:	muli@...ibm.com, jeff@...zik.org, amitkale@...xen.com,
	netdev@...r.kernel.org, brazilnut@...ibm.com,
	netxenproj@...syssoft.com, rob@...xen.com, romieu@...zoreil.com,
	sanjeev@...xen.com, wendyx@...ibm.com
Subject: Re: network devices don't handle pci_dma_mapping_error()'s

From: Stephen Hemminger <shemminger@...l.org>
Date: Wed, 6 Dec 2006 16:58:35 -0800

> The more robust way would be to stop the queue (like flow control)
> and return busy. You would need a timer though to handle the case
> where some disk i/o stole all the mappings and then network device flow
> blocked.

You need some kind of fairness, yes, that's why I suggested a
callback.  When your DMA allocation fails, you get into the rear of
the FIFO, when a free occurs, we callback starting from the head of
the FIFO.  You don't get removed from the FIFO unless at least one of
your DMA allocation retries succeed.
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