Date: Tue, 17 Jul 2007 17:45:30 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: David Christensen <davidch@broadcom.com> Cc: current@freebsd.org Subject: Re: Getting/Forcing Greater than 4KB Buffer Allocations Message-ID: <20070718004530.GV1221@funkthat.com> In-Reply-To: <09BFF2FA5EAB4A45B6655E151BBDD9030483F161@NT-IRVA-0750.brcm.ad.broadcom.com> References: <09BFF2FA5EAB4A45B6655E151BBDD9030483F161@NT-IRVA-0750.brcm.ad.broadcom.com>
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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."
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