Re: [PATCH] fcoe: Reduce max_sectors to 1024

2014-07-10 Thread Christoph Hellwig 
Hannes, can you respin the patch with a comment explaining the limit?

 Does it limit IO size for pass through IO not through block layer ? 

The max_sectors limit also limits the size of passthrough requests.

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Re: [PATCH] fcoe: Reduce max_sectors to 1024

2014-07-09 Thread Christoph Hellwig 
On Wed, Jul 09, 2014 at 08:16:21AM +0200, Hannes Reinecke wrote:
 The DDP offload on ixgbe is only capable of handling requests up
 to 1024 sectors. So we should be exposing this to avoid spurious
 messages about 'not enough user buffers'.

Shouldn't the network driver be able to communicate it's offload
capabilities to the fcoe core?  I'd be happy to take this as an iterim
fix if there's a comment explaining it, but long-term it should be
driver specific.

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Re: [PATCH] fcoe: Reduce max_sectors to 1024

2014-07-09 Thread Hannes Reinecke 

On 07/09/2014 08:18 AM, Christoph Hellwig wrote:

On Wed, Jul 09, 2014 at 08:16:21AM +0200, Hannes Reinecke wrote:

The DDP offload on ixgbe is only capable of handling requests up
to 1024 sectors. So we should be exposing this to avoid spurious
messages about 'not enough user buffers'.


Shouldn't the network driver be able to communicate it's offload
capabilities to the fcoe core?  I'd be happy to take this as an iterim
fix if there's a comment explaining it, but long-term it should be
driver specific.

ixgbe can handle up to 256 sgl elements, but the maximum single I/O 
size is 256 pages. This translates into 1024 sectors.


And seeing that the 'fcoe' driver is effectively tied to ixgbe ATM I 
doubt it's worth investing in yet another callout here.

Intel, can you clarify on i40e? Is it FCoE capable?
If so it might be worth adding a configuration knob here.
Unless i40e has the same limitations as ixgbe ...

Cheers,

Hannes
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