Date: Wed, 21 Aug 2013 08:53:51 -0700 From: Peter Grehan <grehan@freebsd.org> To: Andre Oppermann <andre@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Navdeep Parhar <np@FreeBSD.org> Subject: Re: svn commit: r254520 - in head/sys: kern sys Message-ID: <5214E28F.2060703@freebsd.org> In-Reply-To: <5214DDA4.4010504@freebsd.org> References: <201308191116.r7JBGsc6065793@svn.freebsd.org> <521256CE.6070706@FreeBSD.org> <5212870A.50105@freebsd.org> <521291F1.8060500@FreeBSD.org> <5214D5E0.9040002@freebsd.org> <5214D6CA.2040405@freebsd.org> <5214DDA4.4010504@freebsd.org>
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Hi Andre, > On 21.08.2013 17:03, Peter Grehan wrote: >>> The way to go should be 4K clusters as they are native to the >>> architecture. >>> IIRC a PCIe DMA can't cross a 4K boundary anyway >> >> That's a 4G boundary, for some devices. > > I meant a single PCIe DMA transaction can be at most 4K before it has to > set up another one? 4K is the maximum TLP size but that's rarely (ever?) used - 128 or 256 bytes is more common. A DMA operation is just a sequence of TLPs originating from the endpoint. later, Peter.
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