netdev - Re: [PATCH net-next] net/mlx4_core: Warn if device doesn't have enough PCI bandwidth

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Date:	Wed, 15 Jan 2014 23:15:09 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	Amir Vadai <amirv@...lanox.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eyal Perry <eyalpe@...lanox.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>
Subject: Re: [PATCH net-next] net/mlx4_core: Warn if device doesn't have
 enough PCI bandwidth

On Mon, 2014-01-06 at 21:15 +0000, Ben Hutchings wrote:
> On Sat, 2014-01-04 at 21:17 +0200, Amir Vadai wrote:
> > From: Eyal Perry <eyalpe@...lanox.com>
> > 
> > Check if the device get enough bandwidth from the entire PCI chain to satisfy
> > its capabilities. This patch determines the PCIe device's bandwidth capabilities
> > by reading its PCIe Link Capabilities registers and then call the
> > pcie_get_minimum_link function to ensure that the adapter is hooked into a slot
> > which is capable of providing the necessary bandwidth capabilities.
> [...]
> 
> This is essentially another duplicate of what ixgbe and i40e are
> doing...  (And the out-of-tree version of sfc does it too, but I never
> felt that was ready for in-tree.)
> 
> We ought to have a generic PCI layer function that warns when a PCIe
> device is running below maximum link width/speed.  Maybe even run it as
> soon as the device is enumerated, so that a driver doesn't need to do
> anything.
> 
> Ben.
> 

Hi,

I was thinking about this again, was wondering a few things. Is this
something you were already investigating?

On an implementation note, how would this function know how much
bandwidth a particular device (or function?) would require? I'm thinking
of something along the lines of a driver essentially saying how much the
devices it supports require?

Thanks,
Jake