netdev - Re: network devices don't handle pci_dma_mapping

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Message-Id: <200612071155.23412.amitkale@linsyssoft.com>
Date:	Thu, 7 Dec 2006 11:55:22 +0530
From:	"Amit S. Kale" <amitkale@...syssoft.com>
To:	Stephen Hemminger <shemminger@...l.org>
Cc:	David Miller <davem@...emloft.net>, 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

We can let a driver handle dma mapping errors using these->

1.Reduce the size of a receive ring. This will free some possibly remapped 
memory, reducing pressure on iommu. We also need to printk a message so that 
a user knows the reason why receive ring was shrunk. Growing it when iommu 
pressure goes down will result in a ping-pong.
2. Force processing of receive and transmit ring. This will ensure that the 
buffers processed by hardware are freed, reducing iommu pressure.

3. If we need to do (1) and (2) a predefined number of times (say 20), stop 
the queue. Stopping the queue in general will cause a ping-pong, so it should 
be avoided as far as possible.

-Amit

On Thursday 07 December 2006 06:28, Stephen Hemminger wrote:
> 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.
-
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