Date: Tue, 17 Jul 2007 17:20:28 -0700 From: "Kip Macy" <kip.macy@gmail.com> To: "David Christensen" <davidch@broadcom.com> Cc: current@freebsd.org Subject: Re: Getting/Forcing Greater than 4KB Buffer Allocations Message-ID: <b1fa29170707171720w33c6826ai330aaaa0b03be40a@mail.gmail.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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On 7/17/07, David Christensen <davidch@broadcom.com> wrote: > 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. busdma coalesces the addresses into one segment if they're physically adjacent. Take a look at busdma_machdep.c. -Kip
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