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Date: Tue, 17 Jul 2007 17:45:30 -0700
From: John-Mark Gurney <gurney_j@resnet.uoregon.edu>
To: David Christensen <davidch@broadcom.com>
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Cc: current@freebsd.org
Subject: Re: Getting/Forcing Greater than 4KB Buffer Allocations
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David Christensen wrote this message on Tue, Jul 17, 2007 at 16:54 -0700:
> I'm investigating a problem with my bce driver which occurs when I ask
> for a jumbo
> mbuf cluster (through m_cljget()).  When I map the memory for DMA I
> normally 
> get 3 memory segments (4KB + 4KB + 1KB) on my system, but on another
> user's 
> system he's seeing 2 memory segments (8KB + 1KB).  Is there a
> configuration
> option that allows this or some other tuning variable involved?  The
> system is a 
> Xeon dual-core processor and has 8GB of RAM, running an AMD64 version of
> the kernel.

Is this an issue?  If it is, you need to fix your bus_dma_tag_create
calls to set the segment size and count properly.  bus_dma will get
you exactly what you ask for, and your driver needs to tell bus_dma
what it can and cannot handle.

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."