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Re: [Xen-devel] Swiotlb

  • To: Kieran Mansley <kmansley@xxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir@xxxxxxxxxxxxx>
  • Date: Thu, 05 Apr 2007 16:10:45 +0100
  • Delivery-date: Thu, 05 Apr 2007 08:09:47 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Acd3lJV51EQbQ+OHEdugmwAX8io7RQ==
  • Thread-topic: [Xen-devel] Swiotlb

On 5/4/07 15:23, "Kieran Mansley" <kmansley@xxxxxxxxxxxxxx> wrote:

> While writing a driver for a device doing lots of DMA I've hit an
> "swiotlb_full()" problem.  This surprised me somewhat as I wouldn't have
> expected to need the use of the software TLB - it's a 64 bit capable
> device on a server with only 2 GB of RAM, and so I'd have expected to be
> using a hardware TLB.  Is this a peculiarity of Xen, or should I be
> right to be surprised?
> I expect I can increase the size of the swiotlb to avoid this problem,
> but thought I'd check that there isn't something more fundamentally
> wrong first.

Well, I would agree that it sounds odd. You should definitely investigate --
you don't want to be invoking the swiotlb on the data path for a modern
high-speed device.

 -- Keir

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