Re: [RFC 1/2] PCI-Express Non-Transparent Bridge Support
From: Jon Mason
Date: Mon Jul 16 2012 - 13:55:09 EST
On Sun, Jul 15, 2012 at 05:19:21PM -0700, Greg KH wrote:
> On Sun, Jul 15, 2012 at 04:55:48PM -0700, Jon Mason wrote:
> > On Sat, Jul 14, 2012 at 10:10:15AM -0700, Greg KH wrote:
> > > On Fri, Jul 13, 2012 at 02:44:59PM -0700, Jon Mason wrote:
> > > > +static int max_num_cbs = 2;
> > > > +module_param(max_num_cbs, uint, 0644);
> > > > +MODULE_PARM_DESC(max_num_cbs, "Maximum number of NTB transport connections");
> > > > +
> > > > +static bool no_msix;
> > > > +module_param(no_msix, bool, 0644);
> > > > +MODULE_PARM_DESC(no_msix, "Do not allow MSI-X interrupts to be selected");
> > >
> > > How would a user, or a distro, know to set these options? Why are they
> > > even options at all?
> > Good question. There is actually a potential benefit to disabling
> > MSI-X. The NTB device on one of our platforms only has 3 MSI-X
> > vectors. In the current driver design, that would limit them to 3
> > client/virtual devices. However, there are 15bits in the ISR that can
> > be used for the same purpose. So, if you disable MSI-X, you can have
> > 15 instead of 3.
> But again, how would a user, or a distro, know to set these? Where is
> the documentation describing it? Why really have these options at all
> and not just fix the platform issues (only 3 MSI-X vectors? Really?)
I believe we'll want multiple clients (or have multiqueue Ethernet). I'm happy to add something to /Documentation to describe it and why it would be useful, or I can remove it and re-introduce it when I add multiqueue Ethernet.
3 MSI-X vectors (plus one for PCI-E link up/down) on Xeon NTB, and 33 for Atom NTB. Yeah, really.
> greg k-h
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