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Date: Tue, 08 Mar 2005 22:08:54 -0700
From: Scott Long <scottl@samsco.org>
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To: Mike Silbersack <silby@silby.com>
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cc: Scott Long <scottl@FreeBSD.org>
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Subject: Re: cvs commit: src/sys/pci if_dc.c
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Mike Silbersack wrote:
> 
> On Tue, 8 Mar 2005, Scott Long wrote:
> 
>>  The DC driver asks for an alignment of PAGE_SIZE for data buffers, 
>> but also
>>  asks that each buffer be (2048 * 256) bytes long.  I suspect that 
>> alignment
>>  isn't a real requirement since busdma only recently started honoring 
>> it.  The
>>  size is also bogus.  Fix both of these and stop busdma from trying to
>>  exhaust the system memory pool with bounce pages.
> 
> 
> The requirement as it was originally stated is that they may need to be 
> longword aligned for certain cards.  We handle that in dc_encap already, 
> but I hadn't considered the possible problem with using bounce pages.
> 
> I'll take a look and see if we can determine the alignment requirement 
> before we call bus_dma_tag_create.
> 
> Are there any busdma statistics sysctls that would let us notice that 
> it's being asked to do things like this on a running system?  If not, 
> could you add some?
> 
> Mike "Silby" Silbersack

Yes, the hw.busdma tree has quite a bit of stats regarding bounce page
use.

Scott