netdev - Re: [PATCH v4] net: Introduce realloc_netdev

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Date:	Mon, 18 Jan 2010 10:29:48 -0800
From:	"Michael Chan" <mchan@...adcom.com>
To:	"Jarek Poplawski" <jarkao2@...il.com>
cc:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"David Miller" <davem@...emloft.net>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Jeff Kirsher" <jeffrey.t.kirsher@...el.com>,
	"Peter P Waskiewicz Jr" <peter.p.waskiewicz.jr@...el.com>
Subject: Re: [PATCH v4] net: Introduce realloc_netdev_mq()


On Sun, 2010-01-17 at 14:57 -0800, Jarek Poplawski wrote:
> On Sun, Jan 17, 2010 at 08:56:28AM -0800, Michael Chan wrote:
> > Jarek Poplawski wrote
> > > On Sat, Jan 16, 2010 at 02:50:48PM -0800, Michael Chan wrote:
> > > > The problem with the patch below is that
> > > > dev->real_num_tx_queues can still be reduced during bnx2_open().
> > > >
> > >
> > > I'm not sure I get your point, but there should be no problem with
> > > changing dev->real_num_tx_queues during ->open(). The main intention
> > > of realloc_netdev_mq() is to give drivers some official way to change
> > > dev->num_tx_queues until register_netdev() with the main aim: not to
> > > treat obviously non-mq chips as mq according to netif_is_multiqueue().
> > > Additional gain is memory saved in the case fixed by the patch below
> > > (which btw. waits for some refinement/verification).
> > 
> > Yes, the patch achieves what you describe.  dev->num_tx_queues will
> > be set more accurately during ->probe based on chip type.  In ->open(),
> > the dev->real_num_tx_queues will still be possibly reduced depending
> > on the number of CPU cores and whether we can enable and allocate the
> > MSI-X vectors.
> 
> I wondered, and Peter seemed to confirm, some check whether we can use
> MSI-X could be done during ->probe as well?
> 
> ...
> > > > > + if (!((bp->flags & BNX2_FLAG_MSIX_CAP) ||
> > > > > +      (bp->flags & BNX2_FLAG_MSI_CAP)) || disable_msi)
> > > > > +         realloc_netdev_mq(dev, 1);
> > > > > +
> > 
> > I think we can refine this a little:
> > 
> >         if (!(bp->flags & BNX2_FLAG_MSIX_CAP) || disable_msi)
> >                 realloc_netdev_mq(dev, 1);
> > 
> 
> Hmm... Probably I should use different words. I mentioned above the
> main intention of realloc_netdev_mq() was to fix mq-ness for non-mq
> chips, and this patch demonstrates this. But, there is no reason not
> to fix/optimize more btw. So, I hoped the refinement could also
> include some preliminary MSI-X test etc. Anyway, since I can't even
> test it, I would be glad if you could author something based on this
> stub (unless you think it's enough for now - then I'll send it as is,
> no problem).
> 

It's an improvement over existing code to unconditionally allocate max
tx queues.  To make further improvements, we'll have to experiment with
calling pci_enable_msix() so early during ->probe().  I will look into
it.  Thanks.




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